Internet shocked by teacher's math fail

A teacher's math fail sparked many reactions, and reminded us of one of the most common fallacies.
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[@haus3603]

Ugh, I always hate it when I have to wait 5 minutes so my board is in 1 piece

[@milanfanas]

Yeah, it is annoying indeed. In the morning I have to wait 40 minutes for my table to be in a single piece before I can have breakfast

[@zombination1543]

Lol

[@zedlol5679]

ONE PIECE

[@zombination1543]

@@haus3603 yesterday, my desk was extra hard, and it took me a whole hour to cut it into one whole piece. Ugh, so annoying!

[@rodrigoqteixeira]

Damn, and when I wait 0 minutes and it goes to limbo

[@mhoover]

I was a software engineer for 20 years, 19 of which were spent correcting off-by-one errors 😂

[@bigolbearthejammydodger6527]

I know right - If an off by one error is acceptable to a maths teacher or in presh's case professor... damn home schooling looking like a good choice! (also a life long code monkey)

[@ProuvaireJean]

Are you sure it wasn't 20?

[@igrim4777]

So you were a software engineer for 19 years, 20 of which were spent making off by one errors?

[@mhoover]

@@igrim4777 Come to think of it...hmm... let's see...

[@DerMarkus1982]

That's not off-by-one. That's a stops-vs-stretches problem. "fence-post error" might be more appropriate although "off-by-one" is a fencepost type scenario. Not all fruit are apples, though.

[@ciscou]

There are two difficult problems in computer science: naming things, cache invalidation, and off by one errors.

[@l.clevelandmajor9931]

And you just got one off!

[@ciscou]

@@l.clevelandmajor9931 that's the joke

[@bigolbearthejammydodger6527]

that is going in my memes channel for the work discord!

[@Aphelia.]

good one

[@verkuilb]

If there are two things I’m not good at, it’s counting.

[@jmcdermid]

WRONG WRONG WRONG Marie is ambidextrous, so with a saw in each hand, it only takes her 10 minutes to cut the board into 3 pieces.

[@fgvcosmic6752]

Nah but it does say that they work just as fast, and using 2 hands is working twice as fast

[@reedplaysgames]

Taking into account strength imbalances and bilateral deficit tho it should actually be closer to 15ish lol

[@cocobeans3742]

⁠@@fgvcosmic6752yeah but you can argue the hands are working just as fast, no one said how many hands were working.

[@ironfistgaming8945]

Yayyyyyyy🎉🎉🎉🎉🎉

[@danmessi8142]

Wrong, it never said she was sawing off the board into equal pieces, after making the first cut in 10 minutes she gives up and just cuts the corner of the board making it only around 11 minutes to cut it into 3 pieces.

[@AzureKyle]

Basically, it's a case of misidentifying the x in an algebraic equation. The teacher defined x as the number of pieces, when x is actually the number of cuts. So she started with 2x=10, when it was really x=10. This is a common problem with word problems, where people pay more attention to the numbers than the actual word problem itself.

[@lanarkorras4411]

Yep. That's the crucial idea to keep in mind here.

[@lexlancelian8481]

well, you can use X as teacher used too, but he never realized that she STARTS with one piece (ONE PIECE IS REAL)

[@darnoc0010]

It's called critical thinking and many people never learn it.

[@redstonewarrior0152]

It's kinda like those tests where you are told to follow the directions at the top of the worksheet and most people will just ignore the instructions and begin answering all the questions on the worksheet when the directions just say to write your name at the top of the page, answer quedtion 15, and then turn in the worksheet.

[@AzureKyle]

@@redstonewarrior0152 Especially when some of the directions say flap your arms like a bird or other silly stuff.

[@emeraldaly7646]

This is like that old riddle "If you're running in a race and pass the person in third place, which place are you now in?"

[@igrim4777]

Indeterminate. On a circuit race the persons in first and second places could each pass the person in third place without changing race order.

[@fgvcosmic6752]

​@@igrim4777fine then. You're running on a straight track. Happy?

[@deept3215]

@@igrim4777 They wouldn't pass them, they would lap them them

[@davelordy]

It depends on which direction you're going 😁

[@isaiah0xA455]

@@deept3215 that’s a semantic argument, and a bad argument too. Lapping someone involves passing them *by definition*

[@Jerry_Fried]

I submit that there is no one anywhere who would consider a torus to be a “board.”

[@geraldgomes]

If the board was a square, then the teacher could be right. But the dimensions of the board were not specified and a board is usually not a square.

[@jeremyashford2145]

Submission refused. I would. I would, and do, call a piece of wood of any size a stick. A stick with a hole in it, be it a knot hole, or a worm hole, or a drilled hole, or whatever, is a torus.

[@weevilinabox]

Does this make it more acceptable? Starting with a square or rectangular board, cut a circle (or any other 2-d shape) from the middle of the board, resulting in two pieces with one cut. If the next cut is from an outer edge to the hole in the middle, then there are still only two pieces after the second cut. A third outer-to-centre cut will result in three pieces. Edit: extending this silliness, cutting _n_ non-intersecting shapes from the interior of board will yield _n+1_ pieces. It is then possible to make _n_ further cuts without creating any more pieces, by first cutting from an edge to an interior hole, then cutting from the first hole to the next, and so on. The _n+1_ th additional cut would be from the last hole to an outer edge and would finally generate the _n+2_ th piece. I'm thinking of the hole cuts as being in a row, but I wonder of there's a pattern of holes and joining cuts which breaks this pattern without allowing joining cuts to intersect each other.

[@nicholasreilly3218]

@@geraldgomes And the drawing in the margin depicting the board being cut is clearly not a square, so it is implied that the board is longer than wide, and is being cut at it's narrowest dimension

[@TheEudaemonicPlague]

@@jeremyashford2145 Jeremy, you need education...a torus is not just something with a hole in it. Look it up, learn something.

[@geoninja8971]

Wouldn't surprise me at all.... here in Australia we now have sports teachers teaching maths....

[@MindYourDecisions]

Was it due to budget cuts? But now that professional sports is run by analytics, maybe the sports teachers will be good math teachers ;)

[@Phymacss]

Physics for us😭😭 They bring us teachers who don’t know how to convert between gram and kilogram 💀💀💀

[@ObsidianParis]

Ironicaly enough, a sport teacher would probably have come to the correct solution from the beginning…

[@majinnemesis]

@@ObsidianParis a sport teacher would probably just get a piece of wood a saw and try it out in practice since sport teachers tend to be more physical and like to move

[@laars0001]

⁠@@MindYourDecisionsIn Gr 7 the gym teacher was also the math teacher AND the health teacher, when I was 12.

[@sitnamkrad]

I would not be so kind to give the teacher a break. It's one thing to make an off-by-one error. But the teacher should have had access to the official answers. Especially since the concept of requiring only one cut to turn the board into 2 pieces is the heart of the question. But that's not the only reason. If this was the result of an actually graded test, that means that either not enough students gave the right answer to make the teacher question theirs, or the teacher simply refused to reflect on their own answer. Neither case reflects well on the teacher.

[@neh1234]

To be fair, I don't think any self respecting adult would feel the need to check on the official answers for such an elementary question.

[@Cau_No]

​@@neh1234and that's the reason why so many adults keep being posted on r/confidentialIncorrect.

[@Trozfol571]

​@@neh1234There's a difference between respect and arrogance, the only teachers who never check the official answers are arrogant stuck up teachers who believe that they're right over the students because of some teachers degree, even professional experienced teachers (were I'm from anyway) still check the the official answers and do research cause they have humility and don't close their minds to those they deem inferior to them. It doesn't matter if your older, wiser, smarter, more qualified or better overall than others you can still be wrong and/or misunderstand something as basic math.

[@alihms]

​@neh1234 Not doing any verification is the main reason why people get trapped with one-off error answer. As a teacher, it is her duty to be aware of this type of error.

[@frenchguy7518]

I would only give the teacher a break if they admitted their mistake when it was explained to them, and apologized to the student. Otherwise, they really have no business teaching anything to anyone.

[@nix_]

Fam the way my brain cycled through both answers is something else. 1st I thought, "easy it's 20mins because it's double the time/cuts". But then I saw the numbers 2 and 3 and thought "wait no, it's a ratio" and I worked that out as 15mins. Then I thought "no, that's wrong. It's 10mins for 1 cut, so 20mins for 2 cuts! my 1st answer was right" And all this took place in like a minute.

[@TheEudaemonicPlague]

I find it hilarious that you admit this in public...especially the length of time it took you. It should be dead obvious what the answer is, and only take seconds to recognize. I failed 8th grade general math, and I had the answer pretty well instantly. Of course, I failed because I didn't ever do homework...I could do the math just fine.

[@garrettbates2639]

​@@TheEudaemonicPlague I find it hilarious that you feel the need to put other people down for second guessing themselves, and for not being as good at something as you perceive yourself to be.

[@nix_]

@@TheEudaemonicPlague Calm down, it's not that deep.😂😂😂 But good on you for feeling superior to me and boasting to people about how smart you think you are.👍🏾

[@fuglbird]

I'm glad you took your time and solved the problem correctly. I have helped many kids improve their math. When you stop them guessing, they improve very fast. You have solved it. Go!

[@screw_a_username7491]

@@TheEudaemonicPlague who asked

[@Johnny.Fedora]

It's confusing when you equate the units "cuts", "pieces" and "minutes." An implication symbol would be more appropriate than an equal sign.

[@igrim4777]

Potentially confusing, rather than confusing I'd say colloquial and below standard for a largely mathematics based entertainer where those symbols should have consistent meanings. Expressing this video's duration as 1.243 cuts is open to misinterpretation.

[@xl000]

You can make it somehow work if you consider that you only need off cuts of a given dimension. I know this is not what the problem states, because into doesn’t mean that, but this would make the number of cuts equal to the number of pieces. This may be what the professor had in mind.

[@douglaswolfen7820]

Agreed. It's not ideal. Too many people get the impression that the equals sign means "and the answer is" or "and the next step is", instead of meaning that the thing on the left is equal to the thing on the right I like to see maths as a world of facts that you can explore. You can follow the implications of those facts to find new facts, and investigate wherever you choose. Too many people treat it more like a set of procedures you're supposed to execute, often robotically. They see an equation like "x²=4" and they talk about how you're "supposed" to "answer" it, which is silly IMHO, because "x²=4” isn't even a question i feel like using the equals sign this way contributes to that kind of thinking. But then, that's always bothered me a little about Presh; he seems inclined towards that way of thinking about maths. For instance, he talks about PEMDAS as if it's an unalterable fundamental truth of mathematics, instead of a convention that we use to help us communicate mathematics

[@Tkt-kj8ex]

​@@igrim4777i can feel myself getting smarter reading this...

[@coltith7356]

When I was 11 our maths teacher opened the exercise book, and told the us homework would be from exercise 6 to exercise 17 and asked us how many that was. People were so focused on the fact that it was a lot of homework that they didn't think and all just said 11, to which he replied that it was wrong, and that since we hadn't gotten it right, we obviously weren't very good at maths so he would add exercise 18 too, and asked us how many that was. Everyone was outraged and yelled 12. So he added exercise 19 and asked again. And again. And again. Meanwhile, I was checking the book and didn't really care because I didn't do my homework anyway, so I just wanted to see how hard the exercises were, and they were all very short exercises, that's why he chose that page to pull his prank. Then we got to around 24 when everyone was mad and the teacher just kept adding exercises and the bell had rang, so I asked people to stop saying nonsense and think, and they didn't listen, until we got to 27 and finally I just said 22, he said it was correct and I left while people finally decided to calm down and the prof told them to open the book. This was the biggest main character moment of my life.

[@Zs2324LAMWAIKWANDORA]

gigachad moment 🗿🗿🗿🗿

[@faming1144]

Actually 11 is the right answer. "exercise 6 to exercise 17" does not include 17 itself; that would be "exercise 16 up to and including 17".

[@douglasbrinkman5937]

that teacher has never cut a board in half.

[@Sagryl]

Nope. They spent their childhood and teens being an average/nerdy kid, without doing anything interesting like DIY projects, then cashed in on their lack of ambition and got a teaching degree. And this is where it got them. Yay.

[@lilypad429]

Yeah, they don't have time since they're always waiting to cut a board to one piece

[@davelordy]

The only thing they've ever cut in half is - something something, rhythm of a joke.

[@peterbaruxis2511]

Nobody said half, just two pieces.

[@TayWoode]

@@davelordy.....is a large cake, half for now and half for later coz we all know they’ll be fat with blue hair and a nose piercing

[@7rich79]

The frog in the well threw me off...by one...of your correct answer, but the way I interpreted it the frog had to jump _out_ of the well, not just reach the top of it.

[@brandonfeingold4116]

The frog would have to jump more than 3 feet to get out on day 10, but it is only almost out. On day 11 it would be able to jump out of the hole.

[@7rich79]

​@brandonfeingold4116 yes, that was my reasoning too.

[@futurepath]

You were off by one 😆

[@3057luis]

@@brandonfeingold4116 On day 9 she jumps 3 feet so she is already at 12 feet. 10 days to go out of the hole not 11.

[@tyranmcgrath6871]

@@3057luis Day 9 = 11 ft

[@Benkinjo9419]

This teacher is a perfect example of someone who never understood and thought about topics, just learned them. He simply made the calculation with the time and wood pieces instead of time and the actual work done which is the amount of cuts. No critical thinking, just using the formula. When i was tutoring i always used sneaky questions like this. Makes the kids laugh, a bit angry sometimes, but in the end they not only improve in their classes but learn to think for themselves and ask critical questions. This is something that should be ruthlessly hammered in to ongoing teachers.

[@jbird4478]

I always gave snarky answers to those questions, because teaching math is not supposed to be about trick questions. So in this case I'd write: it depends on the size of the cuts, among other things, but the answer you'd want me to write is 15.

[@bigolbearthejammydodger6527]

As you are a maths teacher I shall re post my comment here for you. Its so Important to teach students when problems can be solved in different ways and when its appropriate to use certain methods. This simple maths questions is deceptive because using simple maths of ANY kind will result in an incorrect answer. As a senior person in industry I have to spend so much time UNTEACHING kids what they have learned incorrectly at school or university! You seem like one of the good ones though so I encourage you to give my analysis of this problem to the kids to mull over - show them that sometimes the obvious calculation problem is actually much more complex in the real world. my comment: This isn't just a MATH TEACHING fail, its a MATH fail. YOU ARE WRONG PRESH! - there is actually insufficient information to solve accurately. This is a systems analysis question - not a maths question - and it must be solved as such! Math with give you a WRONG answer! The job requires you to get a board from location 1(t1), get a saw from location 2(t2), travel to a work bench at location 3(t3) - then set up the work bench to do the cut(t4), then do the cut(t5), then put the tools away and deliver the cut wood (t6) Ie Total Time T = t1+ t2+ t3 + t4 + t5 + t6 whereas for problem 2 its: T = t1 + t2 + t3 + t4 + 2(t5)+Overheads + t6 so in reality its more likely to be about 11 minutes - depending on all the values. You are wrong, the student was wrong and the teacher was wrong - and my answer is only right if i have correctly assessed the problem - which given the lack of detail is unlikely. What you have really shown here is why we CANNOT use maths to solve most real world logistics issues. If we were to use maths to solve this question for a home depot or homebase shop where they cut wood to order it would result in incorrect assessment of the time and loss of money or safety fails.

[@Benkinjo9419]

I should clarify that I am not a real teacher as in teaching whole classes at school, I just tutored and helped kids struggling with their grades in a private institute while studying. Atm I work in accounting and also do a lot of work with new and young hires. Because of that I really loved your comment and especially your phrasing, I couldn't agree more. With this much experience and creative style of thinking I am sure there are a lot of young colleagues really appreciative of you. And I am also very glad for your comment because it called me out for being a fool as well. That "sneaky operating" I mentioned earlier includes deliberately taking a false stance in order to be called out as well. Discovering this kind of thinking for one self and teaching it to the younglings is one of the most important things I believe. Having 5-10 students gang up on you for being wrong, even though there are still another 2 or 3 different "right" answers in the room were always among my favourite moments. In the end the only right answer that everyone could agree on was, that there were no right or wrong answers to these questions, just different ways of thinking. That video reminded me of that and I couldn't resist to let my sneaky side out ^^ @jbird4478, students like you I always liked the most. Nothing better and faster than immediately getting a smug answer to your face when trying to form such a discussion. I hope that you got at least a few thumb ups or even high fives for your answers ^^

[@jeremypnet]

@@bigolbearthejammydodger6527lol. Not a maths question you say whilst using two mathematical formulas to demonstrate how to solve it. It is a maths question, but you have to know what model to apply. Also your model is wrong in different contexts. I’m standing here at my workbench with my saw in hand and my two boards with the places to cut already marked. I’m very untidy, so I never put my tools away and somebody else is waiting to deliver the wood.

[@1947dave]

@@bigolbearthejammydodger6527 The question is about the action of sawing a board, not obtaining a board and saw or doing any of the other preparatory work you have included. In short, you've made the mistake of not answering the question by overthinking it, perhaps deliberately lol. That's why many students fail to finish tests in the allotted time!

[@CalliopePony]

When I read the question my immediate thought was that there's not enough information to solve because it doesn't say if the two boards are the same width.

[@YouTube_username_not_found]

Assuming that those boards have same length and width, there is still no enough information because we don't know the directions of the cuts.

[@josephhaddakin7095]

​@@KZbin_username_not_foundexactly. I thought, 10 minutes to crosscut the board? That's ridiculous. Rip cutting it in 10 minutes, yeah. Then just crosscut one of the ripped cuts. That'd be like 12 minutes, tops.

[@jeffrybassett7374]

@@josephhaddakin7095 Depends. Maybe she was trying to use a hacksaw.

[@cowdyayaad6378]

The question is clear in what it is trying to imply. "If she works just as fast". It even gave a picture of a long board to show that it is cross cut. If a question asks me the speed of light, I will say 3×10^8 m/s. I will add (in vacuum) if I want. I wouldn't say "but you didn't say where so no answer." If someone asks me "where do you live?", I wouldn't say "in my house." You are commiting worse mistakes than the teacher.

[@russman3787]

This kind of argument just feels overly pedantic to be honest. The intent of the question is clear, you are just being a smartass.

[@diegomartinez7180]

The first problem is so badly worded that the answer can actually be "a few seconds" or even "tends to zero", as there's nothing on the problem that binds us to a size of the cuts, and the girl can just saw two tiny bits on a corner of the board and that would still make three pieces.

[@alamrasyidi4097]

it was well visualized though

[@zmaj12321]

While technically true, I don't think I've ever seen an elementary or middle school word problem with mathematically rigorous wording. I think based on the "at the same rate" part of the question, you're meant to infer that each cut takes an equal amount of time.

[@Pond721]

That's not true. It took her 10 minutes to cut it in 2. It clearly states it WILL take her 10 minutes to make at least 1 cut. There's no way it can take less than 10 minutes. The size of the cuts is irrelevant, you ARE bound to 10 minutes.

[@diegomartinez7180]

@@Pond721, no, it actually says "if she works just as fast", so the statement is about her skill, not the duration of the cut, and then it goes to say "how long will it take her to saw another board into 3 pieces", so it actually tells us the original board is different. That's why I originally stated that the wording is inadequate, it's too ambiguous, it can be interpreted however you like.

[@diegomartinez7180]

@@zmaj12321, except the problem never even states it's "at the same rate". It just tells us "she works just as fast", but you're right in one thing, If I had been given this problem when I was 12, I'd probably interpreted every cut will take 10 minutes, so in the end, if my barely adolescent self would be able to not fall into the off-by-one error, I would have arrived to the answer of 20, which is the expected answer, even if the wording is so bad. Yet, the problem is not even multiple choice, so the "line" with the answer can be anything. Curiously, it even makes the very sketchy answer of the teacher possible.

[@levi5073]

How is this complicated??? My God...

[@prevedmedved]

So obvious

[@maxhagenauer24]

It's not complicated, it's just confusing wording and what the question actually means.

[@StevenHughestransportvideos]

It's complicated because you don't have all the information to provide a true and accurate answer. It doesn't confirm the additional cuts needed are the same size, and therefore, it could be quicker or longer for the additional cuts. Simply put, the question is a "how long is a piece of string" question

[@cowdyayaad6378]

​@@StevenHughestransportvideos What is the speed of light?

[@Alexandar358]

It's not it's just an easy trap to fall into

[@dhy5342]

The teacher was counting pieces, the student correctly counted cuts.

[@JLvatron]

In the teacher's defense, the clip at <a href="#" class="seekto" data-time="79">1:19</a> of the person sawing the board, really felt like it was 20 minutes long!

[@thatonefrenchguy937]

But 20 minutes was the student's answer...

[@JLvatron]

@@thatonefrenchguy937 Technically you're right, but it felt like an eternity, lol

[@memyname1771]

It took Marie 5 minutes to find the saw, and another 5 minutes to make one cut to cut the board into two pieces. She now has the saw and another board of the same size as the first board. It will take 5 minutes for each of two cuts to make three equal size pieces. Therefore, the correct answer is 10 minutes.

[@johnburgess2084]

But after making the cuts she has to put the saw away. This takes another 5 minutes because she has to decide where to place the saw so it will take 5 minutes to find it the next time she wants to use it. So, the teacher was right --- 15 minutes!

[@benroberts2222]

Requires making assumptions not stated in the problem. If we need to account for setup and cleanup time the answer is underdetermined because we don't actually know how long that takes; we have one equation with two unknowns

[@memyname1771]

@@johnburgess2084 No, her husband had been using the saw and forgot to put it away, so she had to search for it. Normally, the saw hangs right here next to where she saws logs.

[@memyname1771]

@@benroberts2222 As has been explained by many before me, there are as many correct answers as there are assumptions that can be made to fill in the missing data. Is the second piece of wood the same size and shape as the first? Did she just clip off the corners of the second piece of wood? Was she tired after cutting the first piece of wood? The missing data precludes one correct answer. Therefore, the assumptions I make make my answer correct for those assumptions.

[@Entification]

Why are we shocked anymore? This has happened so much it should be shocking if a math teacher knows basic arithmetic.

[@Erik_Danley]

For the final one about the frog, I was thinking 12ft being the top, that’s not quite OUT of the well, meaning the frog would need another day. But I get the point

[@catcake]

How thick was the wood that it took 10 minutes to saw through? Was the saw blunt? The actual answer is 9 minutes to sharpen the saw, 1 minute to make one cut, therefore two cuts take 2 minutes.

[@l.clevelandmajor9931]

There was nothing about sharpening a blade in the problem. Also, if you've ever used a handsaw, you know most of them don't go dull in just one cut, two cuts, three cuts, or even several more. I am a woodworker, and these are things I know a lot about. I had a hand saw like the one shown in this video for forty years, and it never went dull enough to need sharpening in all of that time.

[@StevenHughestransportvideos]

​@@l.clevelandmajor9931 there is also nothing in the question about size of wood, which would affect the length of time. The true answer is "question needs more details to provide accurate timescales"

[@bigolbearthejammydodger6527]

bingo - this is not a maths question, its a systems analysis and workflow logistics question. using simple maths will give a wrong answer and teachers need to teach students when they can and when they cant use a simple calculation to get a meaningful answer. In this problem as presented there is NO WAY to get a meaningful answer to this question using just maths.

[@chaz720]

"Marie needs to stop skipping pull day."

[@Lylcaruis]

actually its 11 minutes because she needs to sharpen the saw first

[@Chandichada]

This channel is wild. 😂 Sometimes I feel like watching a video about quantum physics is more understandable than what is shown here. Other times, like right now, I thinkk I am watching sesame Street. I love it ❤. Never change📚🤠😂

[@Mr.Starlight_gaming]

<a href="#" class="seekto" data-time="110">1:50</a> luffy proceeds to spawn in.

[@kavinbala8885]

am I cooked for visualizing this happening and laughing out loud

[@mikeguilmette776]

I had the frog riddle wrong, but not because of being off by one . . . for some reason, I assumed the frog would still slide back down at 12 feet. 🤣

[@NichtcrawlerX]

Indeed, reaching the top is not the same as getting out. To get out it needs to have jump distance left, after reaching the top.

[@evknucklehead]

Yeah, part of the riddle specifically said the sliding back happens at night. So if it's at the top on _day_ 10, it wouldn't have a chance to slide back down because it could just hop away before night came.

[@hassanalihusseini1717]

Yes me too! That is ambigious question.

[@scottperry3124]

Two things… The primary problem assumes that one “board” is a standard unit of measure. A “board” could be any number of things. Usually implying longer than wide, but not necessarily in this context. (The example of the square board, is also flawed in that one could cut off a corner and another corner diagonally. Not necessarily at the same distance or angle, making it too nonspecific in my mind.) The frog problem has a similar flaw in that on the last jump that gets him just to the rim of the well isn’t the same as getting out of the well, requiring one more jump.) The issue with word problems is words.

[@WhoStoleMyAlias]

Exactly. Another example, the fence problem was actually given to me as light posts on a street. The thing of course with light posts though is that these are usually not placed ON street corners, but around them. Teacher ended up marking both the intended answer and what was supposed to be the obvious mistake as correct.

[@mohitrawat5225]

Funnily enough once someone commented in one of your video saying that once teacher asked to solve this same question with different values and the teacher did the same mistake but when that person corrected the teacher, teacher's face was worth watching 😂😂😂😂

[@fdmillion]

This is referred to as the fence post problem. Example: If the distance between two fence posts is 10 feet, how many fence posts do you need to make a fence 30 feet long? Answer is clearly 4 posts, but if you don't think about the fact that *each end* needs a fence post, it's easy to just do 30 / 10 = 3.

[@Grizzly01-vr4pn]

Didn't watch the video all the way through before commenting, eh?

[@ItsAsparageese]

​@@Grizzly01-vr4pn Someone got enthusiastic about sharing knowledge and acted on it right away instead of waiting a while first? Unacceptable, better snark at them for it :P

[@Grizzly01-vr4pn]

@@ItsAsparageese Yep, that pretty much sums it up.

[@ItsAsparageese]

@@Grizzly01-vr4pn I'm sincerely sorry for you about your weird priorities

[@Grizzly01-vr4pn]

@@ItsAsparageese Don't be. You have no place being sorry for me nor judging any of my priorities. You deal with your own business.

[@jonahansen]

These are the type of counting issues programmers have to learn to solve quickly and accurately... I know from experience.

[@georgesos]

Teacher had never sawn a board in real life😂😂

[@spicemasterii6775]

She would've torn a piece of paper though

[@bornach]

​@@spicemasterii6775And perhaps sliced a pizza. She might have imagined the board was like a pizza made of wood.

[@MikeTaffet]

One could also take the philosophical approach that you can only ever turn one board into 2 boards. Now you have two new boards, and each one can be made into 2 even smaller boards.

[@graydanerasmussen4071]

-Or you can never cut a board into two, because if you cut a board, you have two HALF boards :D

[@bobagorof]

But the question states that Marie *can* turn a board into pieces of a board - so whether you or I are capable of it is irrelevant. Marie has the ability to do so.

[@graydanerasmussen4071]

@@bobagorof Spoilsport! Ruining a perfectly good philosophical discussion :D

[@Duke_of_Lorraine]

That's why you shouldn't dive head first into numbers and think about the problem in practical terms, when possible.

[@mathematicskid]

<a href="#" class="seekto" data-time="68">1:08</a> eventually everyone saw 😆

[@narfharder]

Good catch. I aspire to be you. IOW I saw what you did there.

[@objectmountainstudios]

This channel is one of the reasons why I love math.

[@RGP_Maths]

The most noteworthy off-by-one error: people who celebrated the END of the 20th century at the BEGINNING of year 2000.

[@pysaumont]

The last one is wrong. Assuming (for simplicity) that nights last for 12 hours, the time needed for the frog to get out is 10 x 12 + 9 x 12 = 228 hours = 9.5 days

[@Carlos59706]

Interesting option, but i think there is not enough information to assume that the frog take 12 hours to jump because is not specified. "Every Day" means just to the number of the Day in which the frog is regardless of the hour, so i think 10 days is more correct, but even if you assume that frog jumps at first hour of the day, the answer will be 9.25 days, since the daytime starts at 6:00 am.

[@dentonyoung4314]

2 pieces = 1 cut, 10 minutes per cut, so 2 cuts = 3 pieces = 20 minutes. How did the teacher bollix this up?

[@_Codemaster_]

Well, because the teacher wasn't the sharpest tool in the shed.

[@jmkqfnvyl87]

Mary also needs to have her saw sharpened. . . 😅

[@randomperson2160]

Because the teacher took 10 minutes and divided by 2 to get 5, then multiplied by 3 to to get 15. Not realizing it is not the number of pieces but the number of cuts.

[@BobFitchKSP]

As a woodworker I can tell you that cutting a board that’s half as wide will not take half the time of the wider board. It’s way more than half, but less than the original. Each stroke of the saw cuts a certain depth. It’ll be closer to the original board time, as long as the saw can stay on the board for its entire stroke. Unless it’s a bandsaw or table saw… then maybe it’s half the time, not counting setup time, but the picture shown was of a handsaw.

[@Pokerjinx]

<a href="#" class="seekto" data-time="494">8:14</a> actually, that's not the best way to explain this one. If you watched seasons 5-11, that means out of 11 seasons, you didn't watch 4 of them (seasons 1-4). Therefore, if you take the total number of seasons, 11, and subtract the number of seasons not watched, 4, you get 11 - 4 = 7, which means you have watched 7 seasons.

[@Bomartins]

Good point. There's also some variability in the interpretation of the phrase "5 to 11". You can argue that '5 through 11' means you watched the entire 11th season.

[@desertdarlene]

I saw the problem right away and got 20, too. It took 10 minutes to make 1 cut, then it would take 20 minutes to make 2 cuts. It's all about wording.

[@Chris-hf2sl]

Quite amusing. However, one thing I noticed was that the question said "board" not "log". There's a difference. At <a href="#" class="seekto" data-time="234">3:54</a> in the video, he actually cuts a square board rather than a log. 1 cut takes 10 minutes, then in another 10 minutes he can make a cut at right angles to the first one and get 4 pieces in 20 minutes rather than 3 pieces.

[@Grogir]

<a href="#" class="seekto" data-time="520">8:40</a> you can cut the log in 12 equal pieces with just 4 cuts 🤓

[@wendyheatherwood]

True, but each time you double up the cut log you're also doubling how long it will take to make the next cut.

[@edsznyter1437]

@@wendyheatherwood Shirley, he's talking about cutting the log lengthwise twice then making the original two crosscuts. The question is so poorly stated that we can't determine how long that would take.

[@a-british-villain]

​@@edsznyter1437 but then it will take longer because the cuts aren't equal in size.

[@seanrodgers1839]

In computers, we start an index with 0, so at 15, we have a count of 16. I'm very familiar with the off by one issue.

[@sportbikejesus]

fence post issues in computer programming are not always related to that. Beginner programmers are taught to remember that counting is inclusive where subtraction is not. eg, `seq 1..5` will produce 5 iterations, not 5-1 iterations.

[@lucestrasz2312]

It takes a teacher 10 minutes to grade a two-question test. How long would it take the same teacher to grade a three-question test? - A better question to ask for this teacher.

[@anotherpromotor]

The off-by-one error is one of the most annoying fallacies I've ever seen. No matter how hard I try to explain it, they will never understand

[@Woad25]

Maybe you need to explain it one more time?

[@DaddyBiscuits]

There's a particular time in a childs' education where it's really hard to teach them music theory, because in music, there is no count of zero. Music counts begin on 1. Same goes for days and months, but not hours.

[@OpenTanyao]

<a href="#" class="seekto" data-time="715">11:55</a> Your answer is actually off by 1 here. The frog starts with a jump on day 1, which takes 0 days. On day 2, the frog jumps to 4, so it took 1 day to get to 4 feet. That means that if the frog jumps to 12 on the start of day 10, it took 10-1 days, so 9 days.

[@Epoch11]

I thought the answer was 9 as well

[@jzheng7324]

I think you misinterpreted the statements. ONE DAY is corresponding to ONE JUMP, which means it takes 1 day to make a jump, or once jump, the day ends. You can follow the steps below. Let POS be the current position of the frog, START be the starting position, and DAY be the days it spends. The frog starts at POS = 0 (START = 0), the days it takes is DAY = 0. 1. START is equal to the maximum between 0 and POS-2, since when the frog is at the bottom of the well, no slice off/step back. (START = MAX(0, POS - 2) ) 2. Jump 3 unit up. (POS = START + 3) 3. Increase the DAY it takes by 1. (DAY = DAY + 1) 4. If POS is not equal to or greater than 12 (POS >= 12), back to step 1.

[@OpenTanyao]

@@jzheng7324 If it takes 1 entire day to jump (I don't know if you've ever seen a frog jump before, but let's grant the anti-gravity frog in this case) and 1 entire night to fall back, then the answer is 9,5 days, because the following night doesn't matter anymore. So off by 1 night in the low gravity case.

[@gorilladisco9108]

You guys forget that Marie spent 5 minutes meditating and contemplating, then the other 5 minutes for actual sawing. So if she had to saw the wood into three, she would need 5 + 5 + 5 = 15 minutes. :p

[@braindamage7311]

It also depends on the shape of the cut (the exercises doesn't specify the board is being cut equally). The schematics in math exercises are usually not accurate, so I ignored it and imagined a very thin board of large length and hight. You can think of many ways to cut the board. Some cuts will be faster than others.

[@ChatBot1337]

A.. teacher? A.. human? I have no faith left. If it takes me ten minutes to drive somewhere, round trip is then.. 15?

[@XJWill1]

I'd say the answer to the frog problem, as stated, is best given as 9 days. Yes, it would reach the top at the beginning of the tenth day, but since it is the BEGINNING of the tenth day, the duration of time was 9 days, assuming it started at the bottom of the well at the beginning of the first day.

[@tanvirrahman7339]

Day 1 starts are 0ft and ends at 1ft after the night so at the start of day 2, the frog is at 1ft. Day 9 starts are 8ft and ends at 9ft. Day 10 starts at 9ft, jumps 3 feet and frog is at 12 feet now. There is no indication on how long it takes to climb 3ft. 10 days is still the correct answer.

[@Becky_Cooling]

If we assume that the well is dry, the frog will dehydrate and die after about 7 days,

[@XJWill1]

@@tanvirrahman7339 No, it is 9 days. The frog "jumps", it does not climb. So at the beginning of the tenth day, it jumps to the top. So the time to get out is 9 days plus the length of time to jump. Any reasonable interpretation would put it at 9 days plus 1 second or so.

[@MrDannyDetail]

@@XJWill1 I don't think the frog is making a single 3 foot jump each day and then thinking 'job done until tomorrow'. I think the 3 feet is the overall progress it can make from a whole day's worth of jumping up the inside wall of the well. By that interpretation it gets out just before nightfall on day 10, so a duration of 9.5 days (or something in that region) could be argued to be the answer.

[@kmbbmj5857]

I have a different interpretation from that. When the frog jumps from 9 feet, it reaches 12, which is equal to the top, but not above the top so it is not out yet. It takes one more day to jump above the top and therefore out of the well.

[@1a1u0g9t4s2u]

Another example of ‘off by one’ is to count backwards from 10 the number of fingers ( and thumb) on one hand. Answer is 6. Then add 5 as that is the number of fingers ( including the thumb) on each hand. 5 + 6 = 11 therefore you have 11 fingers and thumbs.

[@AntiWareWolf]

there are 2 ends on the teacher spectrum

[@BrazilMentionedHueHue]

Love and fear

[@reubenmanzo2054]

I had a situation like that. The question was as follows: A ship is sailing due south. It turns to sail north east. Through how many degrees did the ship turn? The correct answer was listed as 45, with a diagram of the ship's travel path given as reasoning.

[@rhpmike]

I was wondering how you were going to make this question take 12mins.

[@bkucenski]

Teachers like this make students feel like they can't do math when it's the teacher who can't teach. Teachers always need to have the answer key to avoid brain farts like this.

[@DrakonLameth]

I could be the smart-alec-in-class on the well point and argue 11 days for the same reason I'd tell someone who said 12 was off by one on their thought -- the well is 12 feet deep, so on day 10, the frog makes it to the surface, but doesn't leap *clear*, it leapt *to* the height of the opening, so one more day to jump clear. (Maths as "starts at -12, +3 jump, -2 slide, must reach higher than 0 to escape")

[@brianschuetz2614]

That actually crossed my mind as well.

[@dentonyoung4314]

With the "murdoch mysteries" one, my brain automatically went "there are 11 season, and he didn't watch the first 4. 11 - 4 = 7."

[@trevpavey3505]

<a href="#" class="seekto" data-time="494">8:14</a> you could just do one extra cut from 5 cuts or 6 pieces for 6 cutsfor18 minutes because the question doesn’t say they all have to be vertical or horizontal

[@Kalimangard]

I'm not sure which is more embarrassing for the teacher: Claiming that the time needed was a constant multiplied by the amount of pieces you get rather than the amount of cuts you make or the statement "10=2"

[@Camelad]

The frog in a pit problem is under specified. Is the frog at the lip when it jumps day 10 and falls back 2 feet so it must jump again on day 11? Or is 12 feet actually out of the pit? The problem as described is not clear. Do you need to exceed the height? Or just meet it?

[@philrod1]

I got 11 for the frog problem. I worked backwards from the assumption the frog would need to get to 10 feet before it could jump _higher_ than the 12 foot well and escape. So ten days to get to 10 feet, then escape on the 11th day.

[@rymixxx]

Aye same. On is not out.

[@scmtuk3662]

I wonder what the teacher would have said if they were asked "So, how does it take 5 minutes to saw a piece of wood into one piece, if there is already one piece?"

[@mjbalbo]

Maybe it was an infinite board and the sawer was taking pieces out of it 😅

[@cptfwiffo]

Wait... If you cut a log 2 times, you then put it in its end, cut it twice, and youre left with 12 pieces. Also, if you cut a square in two, one can be infinitely small in width, leaving you with a cut time of almost zero

[@davidtsang4949]

I made the same mistake. My issue would be how the question could be framed to make it more apparent.

[@ironfistgaming8945]

It IS apparant

[@gorilladisco9108]

The question can't be any more clear.

[@MrRAGE-md5rj]

@@ironfistgaming8945 Clearly you've never sawed a board before.

[@ironfistgaming8945]

@@MrRAGE-md5rj clearly you've never solved maths questions

[@ironfistgaming8945]

@@gorilladisco9108 exactly. the question is literally sending the message that it wants to send. it IS an understandable question man. its not even worth making a video about, its just that the teacher fumbled it for once, and I am sure the teacher must have himself/herself realised his/her mistake soon after.

[@dawsonwu7272]

Its so annoying having to cut my board into one piece even though it's already in one piece with zero cuts

[@All4mula]

10 mins because she did it just as fast

[@_Vengeance_]

Ah, I see the teacher's mistake. The experience from the first cut will speed up the second cut. However, the dulling of the saw will slow down the second cut, evening out the speed-up from the experience. The teacher forgot to take the dulling of the saw into account.

[@KenPaulsenArchitect]

Season 5 TO Season 11 is 6 segments. Season 5 THROUGH 11 is 7 segments.

[@pandoratheclay]

5 to 11 = 5, 6, 7, 8, 9, 10 5 through 11 = 5, 6, 7, 8, 9, 10, 11

[@_majortom_]

This video started with a simple problem, but progressed to much higher level. Very nice one.

[@OweEyeSea]

I realize the crazy stretch of saying the wood was in the shape a doughnut to explain how the teacher really was right is tongue in cheek. But I couldn't help but think of Trump hiring this person to come up with justifications for all his wrong answers a la "SharpieGate".

[@seanrodgers1839]

For the 2nd one, cutting the small piece in half, it would be less than 15 minutes. The second cut is a rip cut, which will saw faster than a cross cut.

[@janofb]

These are the same teachers striking for more pay.

[@stevenmayhew3944]

That would be like drawing a music staff with only four bars and expecting it to have five spaces in between the four bars. You only have three spaces, which is why music staffs are drawn with five bars and four spaces, instead.

[@SmoMo_]

I think the teacher just read the question to mean there is a big plank of wood, and it took 10 minutes to cut off two pieces. It makes perfect sense now why the teacher would think it takes 15 minutes to cut off 3 pieces. To avoid that misinterpretation and to test the student on the intended maths it could be re-worded “It took 10 minutes to cut a plank of wood into 2 halves, how long would it take to cut a similar plank of wood into 3 thirds” So, I think your conclusion here about it being an off-by-1 error isn’t likely to be correct for this particular question.

[@the4spaceconstantstetraqua886]

cut off ≠ cut into good observation though

[@st-gelaisrene3287]

Fot the frog question. There is no day zero. On day nine the frog is at 8 feet. On day 1 the forg is at zero feet and reaches 3 feet, on the morning of day 2 the frog is at 1 feet and reaches 4. On the morning of day 3 the frog is at 2 feet and reaches 5 feet and so on. On the morning of day nine. the frog is at 8 feet and reaches 11. On the morning of day 10 the frog is at 9 feet and reaches 12 feet. So it takes nine days and a few minutes or 10 not full days. Same answer but no 9 feet at the 9th day.

[@dw8931]

A teacher lacking education. Guess what happens to the pupils. Society is doomed...

[@204trebor]

My questions is. Why does it take Marie 10 minutes to cut a piece of wood. It should be done in under a minute. The question should be if she works just as SLOW, how long will take her to saw another board in 3 pieces.

[@professorlilith5933]

So many assumptions here about an unnamed teacher and this random partial view of an arithmetic problem that appears to be a photocopy of mimeographed copy.

[@Poldovico]

the homework wasn't developed wrong. The teacher just didn't look at the answer key.

[@professorlilith5933]

@@Poldovico Tell me you've never done lesson planning without telling me.

[@Poldovico]

@@professorlilith5933 tell me you didn't watch the video with direct evidence without telling me

[@michaelmetcalfe639]

And this is where application and theory collide and create the big bang

[@smylesg]

Also, the question states "it _took_ Marie ten minutes" not "it _takes_ ..." Maybe she went slowly the first time around.

[@MikeTaffet]

“If she works just as fast”

[@oribraverman9657]

Based on the diagram, 11 posts are needed to cover 30 feet if spaced every 3 feet. However, if you consider the length of each post, the number might change.

[@timeonly1401]

If this straight fence were being erected on a VERY SMALL planet who's circumference is 30 feet.. the builder could use the 1st fence post as the last, and the answer would be 10 posts. LOL!! 😂

[@oribraverman9657]

@timeonly1401 Haha, that's one creative way to solve it on a small planet! 😄 But what if the post itself is 30 feet long? Then you'd just need one post and problem solved, no need to go around the planet twice! 😉

[@Rayleigheffects]

I can confidently confirm that the amount of off by 1 errors I have made can fit on a 30 metre wall if they are spaced out every 3 metres.

[@FarrizWil]

The mistake is to count the pieces instead of to count the number of cut. Two pieces means one cut, 3 pieces means 2 cut. With one cut (2 pieces), it takes 10 minutes. So if Marie wanna make 2 cut (3 pieces), it will take 2× 10 minutes.

[@billpg]

<a href="#" class="seekto" data-time="700">11:40</a> Question says that *every day*, the frog falls back two feet. Not every day until he gets out. The answer is that the frog never gets out because he's doomed to forever jump out and fall back in again, ad infinitum. Why yes, i am very clever. Thank you for noticing.

[@timcoley646]

It's 15 minutes because she already found the saw.

[@EllipticGeometry]

I built my ‘straight’ fence along a geodesic on a much smaller planet. Joke’s on you.

[@bastiaan0741]

The question implies equal cuts and pieces. If not, you can chip an edge off to obtain a piece in 1 minute.

[@tomascernak6112]

If i made such mistake as a teacher, i would not only quit at that school, but i would stop teaching at all out of embarrassment.

[@EdwardCurrent]

Especially since there was an answer key! I think it's fake.

[@christianbuche9244]

That reminds of what's called "Zaunpfostenproblem" in German (literally "fence pole problem"): You need n + 1 poles for a fence of n units in length

[@artex98]

The answers from <a href="#" class="seekto" data-time="210">3:30</a> to <a href="#" class="seekto" data-time="325">5:25</a> can be disregarded because you continue to saw the same board while the problem explicitely says "another board". Additionally you have to assume both boards are the same size and thickness (otherwise the problem cannot be solved), so the time effort for each cut is identical.

[@danteeightsix9069]

A major off-by-one was that the 21st century and 2nd millennium started on 2001, not 2000, since there was no year 0. Just made another off-by-one error. It would be the 3rd millennium.

[@TheOtherBill]

Suppose the fence is between 2 buildings 30 feet apart. Realistically a fence or railing ending at a building would end at a split post fastened to the building, so you'd use 10.

[@GothicFarmsGaming]

I've seen the off by one error at my job. They are trying to trying to get a count of boxes using the box numbers in a range that doesn't start with one. Take the highest number and subtract the start and boom, off by one box.

[@oso1248]

Whether I forgive off by one errors depends on what you’re doing? Are you a teacher? An engineer? An air traffic controller? You get no forgiveness unless you change careers as you are not suited for your profession.

[@rolliebear42]

I had an answer before you finished reading the introduction. I work in TV, I prep and air syndicated programming. I just picked it up one day.

[@thechumpsbeendumped.7797]

If it takes Marie to saw a board into 2 pieces... She's holding the saw upside down.

[@HrKCA]

5 minutes to go find the saw, 5 minutes for each cut. Makes sense to me.