A Simple Riddle You Probably Will Get Wrong. The Watermelon Paradox!

Even people who have PhDs in science get this simple brain teaser wrong! Can you figure it out? (It is also known as the potato paradox.)
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[@matthewedwards9423]

This sounds more like someone trying to come up with an excuse for why they ate half the melons on the train.

[@micahlong2073]

But only the water!

[@mayukhintesarislam306]

lmao

[@NetherFX]

❌i've done half my tasks ✅my performance went from 99% to 98%

[@HxTurtle]

not the same statement, though.

[@TheTrueM4gg0t]

Not quite. Like this: ❌ Boss, I sleep only 98% of the time on the job now, instead of 99%! ✅ Boss, I doubled the amount of work I complete every day, I need a pay raise! 💸

[@kubastachu9860]

@@HxTurtle yeah, more like "I'm doing less than half the work but only lost 1% of performance, yikes!" followed by "but why do you let me go with such good stats? Lost trust? How am I not dependable enough to not assign those tasks?"

[@PeterFrancisFernandez]

The false assumption is that there is a 1% loss of water versus the original weight, when in fact it is only a ratio. Using that it becomes easier to understand that youre trying then to work out what weight fits the new ratio rather than thinking of it as having lost 1% of water

[@TheOreoOverlord]

Yup, once understanding this, the problem becomes much more simple and obvious. Took me some time though because it's worded(quite well) to lead you to believe the % is not a ratio but rather an ammount

[@Christopher._M]

I knew it felt like I was missing something when it first thought about it. Which is why I was sure you would have to solve algebraically to get it but it's such an easy assumption and mistakes to make if you just read it

[@senseibear2436]

Somebody is cheating here with the wording! I could have sworn the video said 99% of the total weight (100kg) was water.... Or is that what the listener just infers themselves, hence the riddle? It just sounds like the person removed 1.01% of the total weight...

[@stevemaurer8120]

It's not a "false assumption". It's an incorrectly specified problem. And that's the real answer: "As specified, this question is too ambiguous to solve".

[@brevitygreaves2321]

"dropped to 98%" means what? Is there an actual 1kg watermelon anywhere in the world such that, upon extracting 1% of its water content, its weight magically drops to 50% of its original weight?

[@PugganBacklund]

my mind went: melon went from 1% -> 2%, doubeling, so weight must be half. then i started think, what did i miss..

[@vt2788]

You are just genetically superior

[@southernbreeze3278]

didn't make sense to me 'till I read this comment

[@emad3241]

you got lucky

[@marvhollingworth663]

You missed nowt, that makes perfect sense.

[@user-jc2lz6jb2e]

You focused on what WASN'T water, yet the water is the focus of the question (all the information is in terms of it). People think "oh 99% to 98% isn't much loss", and that's where they get tripped up.

[@Ynook]

The way I see it basically what you did in the end. If 1 Kg of watermelon is now 2% of the weight, the total weight is 50 times 1 Kg.

[@theglobalwarming6081]

I solved this myself. I am both confused how much weight was lost but also it kinda made sense

[@scottmcmillen3015]

Your method is far more intuitive to me than the ones Presh started with. First notice that 1%, hence 1 kg, is not water. For 98% water, we ask: “1 kg is 2% of what?” This question gives the intuitive answer 50 kg, or can be translated into the equation 1 = .02x, and hence x = 50 kg.

[@ModelLights]

@@theglobalwarming6081 'I am both confused how much weight was lost ' Realize, there's an easier way to see the reduction in weight, take it further. 1kg solid and 99kg water gets the 99% water content. But to get to 50% water content, you have to have the starting 1kg solid, and only 1kg water left. You have to lose 98kg of the initial 99kg to get down to 50% water content. The water content percentage being referenced to the 1kg solids instead of an independent reference means the scale slides, and by using 1%/99% to start, the scale slides very hard. 99 kg of water is 26.12137 gallons. Take five 5 gallon buckets of water and another gallon, put them together, and try to wrap it all and hold it together with only 1kg of watermelon skin and rind. It's a not real problem, specifically chosen to use the self referencing 'water content' with an unrealistically high water content to generate the huge swing in values. It could work in some less familiar things, but you would be hard pressed to do this with a watermelon. Real watermelons tend to be 4% or so solid, they'll be mush before you get to 1%.

[@michaelallen1432]

That's pretty much what I did. The water is the thing that changes and it's the unknown. But the mass of everything else is the same before and after. You start with 100kg total, 99% of which is water. So everything else is 1kg. The amount after, is still 1kg. You are told that the water content drops to 98%. So that means the percent of everything else is 2% Knowing that the amount of everything but the water is 1kg, and that the percentage of it is 2% , you can then calculate the total mass of everything as 1kg/0.02 = 50kg

[@beepbop6697]

​@@ModelLightsfrom what I'm reading, watermelons are 92% water. Perhaps if you remove the inedible green rind then the editable red stuff is 96% water...

[@budsellers]

Your math solution is correct, but that freight shipping cost will be wasted because the load of watermelons are useless now

[@martinprince8253]

Watermelons that are twice as sweet? gimme gimme gimme

[@dirkbester9050]

Not at all. You can still make watermelon skin jam from it, and the concentrated watermelon juice can be drinkable. If it is not some kind of maidenless pit free melon, you can plant the seeds next year. Unless it also rotted. That would leave you with making some watermelon wine or vinegar at best.

[@wideeyedraven15]

They are not useless.

[@angrytedtalks]

Bowling balls.

[@adb012]

The watermelons will not be dry. They are still 98% water. And they will be twice as sweet and flavorful.

[@mickdavies5647]

They are students at a barbecue. I can think of several reasons why they got the answer wrong, ranging from 4.5% to 40% in volume 😂

[@cparks1000000]

😂😂😂 Some even 65%.

[@TitularHeroine]

😂😂

[@hedgehogclaws8877]

This was actually hilarious

[@jimmyh2137]

I can thing of some other reasons. More... plant based, let's say.

[@theoroth6515]

From 6:26 to 7:07, there is the expression "d=0.1(100)=1" but it should be "d=0.01(100)=1"

[@MichaelPiz]

But how old is the driver?

[@isambo400]

And how freshly does his toad walk?

[@Bob94390]

Because he has neither a fish.

[@dirkbester9050]

The driver is 98, but real thirsty!

[@Sqrt.Infinity]

But how old are the watermelons?

[@milanstevic8424]

But how many watermelons were there?

[@k1ry4n]

If the non-water content goes from 1 (1% of the original mass) to 2% of the new mass it means that we lost half of the original mass. If 1 kg now is 2% the new mass is 50 kg.

[@aidanhammer6968]

This is a much clearer way of framing it.

[@k1ry4n]

@@aidanhammer6968 The explanation in the video seems to me unnecessarily complicated.

[@SigFigNewton]

Wow. Nice! I wrote out three very simple equations with three variables and did the algebra

[@SigFigNewton]

Looks like the video basically did what I did. U making me feel foolish

[@ExtraTrstl]

This helped, thank you!

[@shivanshukantprasad]

Calling veridical paradox a paradox itself feels like a veridical paradox.

[@9_1.1]

simple explanation: assuming the non-water part of the melons didnt change, that part is still 1kg. that 1kg is now 2% of the total mass, or 1/50th, meaning the rest is 49/50ths, or 49kgs.

[@wild_insomnia]

damn,but it's headscratching how flabby dried out potatoes can still consist of 98% water...That's something surreal...

[@jensraab2902]

To be honest, a "potato" containing 99% or even "only" 98% of water wouldn't be much of a potato. Even watermelons, according to Auntie Google, don't consist of 99% water. The figures I found on the quick was 92% water in a watermelon, and 80% in a potato.

[@beepbop6697]

... And adult human male is 60% water

[@tomdekler9280]

@@beepbop6697 Well yeah, both give a big wet splat when you chuck them out of a 12th story window.

[@MachineCake]

I think one reason for the confusion by many people is because they (like I did initially) interpret the "water content" as a percentage of the VOLUME instead of the WEIGHT. I pictured watermelon-shaped containers 99% full of water changing to 98% full of water, which is a different problem. :P

[@LLlAMnYP]

What changes if it's volume? Just like weight, the overall volume would reduce as well.

[@lifeisajourney4340]

@@LLlAMnYP Bro, What if it was 98% water, 1% Dry stuff, 1% Vacuum? Consider the watermelon is a closed system.

[@LLlAMnYP]

@@lifeisajourney4340 > watermelon is a closed system Awww, hell no it ain't! XD

[@lifeisajourney4340]

@@LLlAMnYP What about the other question?

[@RedFloyd469]

@@LLlAMnYP if it's just a single percent drop in volume, there is no guarantee it would equate to 50kg, or 40kg or 37kg, or anything, because we don't know what the volume to weight ratio is. This was my problem too, and couldn't seem to solve the equation this way.

[@sheshakrishna1111]

Chemical Engineers: Material Balance....

[@sauerjoseph]

Yes, as a fellow ChemE, I was thinking the same thing. This is what we do every day. No decent ChemE should ever get this wrong! We know from experience how much minor changes in %concentration can make such a huge change in lbs total removed. Presh could have plotted an X-Y chart of "Change in total weight" VS "Starting %Water" (1% drop in %Water at each point) and use this to show how this 'change in total weight' heavily depends on the starting %Water.

[@educassus]

I came here to say the same. Before becoming a ChemE, I solved problems like this using cross multiplication when I was studying for my technical level degree in Chem.

[@ThinkOpenlyAtGMail]

You have the calculation of "final dry weight" misrepresented at 6:34. It shows "d = 0.1(100)", when it should show "d = 0.01(100)". (FYI)

[@ralanham76]

For me the visual part makes sense if the dry weight was 2 yellow dots with 98 blue then " simplify" to 1 yellow and 49 blue.

[@melissascheid841]

You forgot to ask the fundamental question, " What is the definition of water content / moisture content?" In soil mechanics, the definition of moisture content is the mass of the water divided by the mass off the solids. With this definition, you get very different results. This definition results in the mass of the solid to be 50.25 kg and the initial mass of the water to be 49.75 kg. The final mass of the water is 49.25 kg resulting in a final mass of the melon to be 99.50 kg.

[@mab06]

Nonsense. You have inented an ambiguity that does not exist.

[@M1412B]

In the Netherlands this problem was presented about 20 years ago on a national IQ test TV show as a stallholder selling 200kg of cucumbers on a hot day. I remember being stunned by the answer as it is so counter intuitive.

[@marcusscience23]

One way to think of it is that the percentage of dry weight goes from 1% to 2%, so it doubles. Along with the fact that the amount of dry weight remains constant, in order for the percentage to double, the total weight must halve, so the final weight is half of 100 kg, 50 kg. 50 = 100/((1-98%)*(1-99%))

[@Stooge2]

That makes so much sense, thanks!

[@jamesdlin7]

Yes, I think it's interesting that reformulating the question to be "the dry weight percentage increased from 1% to 2%" probably would produce much different results.

[@ListentoGallegos]

I love questions like these because they expose many people to the realization that their intuition is misleading.

[@SpiritmanProductions]

I found it much easier to solve by looking at the dry weight, which doubled from 1% to 2% of the total, so, because no new dry weight could be added, the total must have halved.

[@cookesam6]

Man it makes you feel good when you get these right

[@ericaheathrow7085]

The shortest way to reason this is not to do any actual maths: use logic instead. Ask yourself not what has changed, but what *hasn't* changed; what hasn't changed is the amount of *hard* material. In the initial situation, 1Kg of hard material was 1% of the total. In the end, the same 1Kg is now 2% of the total; if 1Kg is 2%, then the total weight is 50Kg. (1 Kg hard material, 49Kg water) No actual serious math necessary, just quick logic. Going into algebra and variables and all of that is a very spoon-digging way of doing this, when using simple logic takes seconds.

[@A-Negative]

I hated math, algebra, and calculus. Until you walked through this problem. Wow. I clearly had subpar teachers. Perhaps I would have stayed in the science field. Kudos.

[@baze3541]

I had the worst math teacher in high school and yet that did not hold me back from math or anything

[@MarcoMagallanes-p2w]

​​@@baze3541Same my math teacher in highschool was so strict that everyday the test is different from what.we learned which yeh it's just so strict and evil She told us to advance in the book And she gave us a test that wasn't In the book and yeh I call her evil and strict

[@jonahansen]

Yeah, well I loved science and math, but I often see arguments that make something so clear I realize my teachers were not all first class. The super-great teachers are few and far between, but could really improve the learning for students having a hard time. I suppose that is the mark of a good school, where the school recognizes and hires the best teachers.

[@FreyGrimrod]

A PhD doesn't mean you are smart it means you are determined and willing to be hazed with trauma.

[@harisimer]

No, a PhD shows a special aptitude for scientific work and research. If you are smart that very well might make a difference

[@Kupferhans]

@@harisimer I think both cases exist. It would be ideal if everyone had a special aptitude for scientific work. But many people just want to have the degree because it helps them with their carreer and so they torture themself through it.

[@yippee8570]

Oh there's an American politician with a PhD who used the slogan 'Jesus, Babies and Guns' - I forget her name - and who believes the earth is flat and that we live in a 'globe conspiracy'. That might just be a reflection on American universities, I don't know...

[@woodward4789]

Imagine losing 50kg of water to summer heat. Those melons must be shrivelled messes

[@verkuilb]

It becomes easier to visualize, if instead of saying “99%” and “98%”, you say “99/100ths” and “49/50ths”. Still challenging for many, but that difference in the denominator helps some people.

[@Keixxo]

When you first started explaining the answer, I was so irked, because I was sure that was wrong.

[@PKua007]

I didn’t expect that low mass at the end, but I knew you couldn’t just subtract 1kg, so I decided to write it down and solve it carefully and got the correct result

[@geoninja8971]

Very cool. I started writing some equations, and soon worked out to convert everything to % of solids, then it all fell into place....

[@p.g.8796]

The "problem" that I have with this, is the fact that we are looking at the final water percentage (98%) rather than what is lost from the original part (99% off 100). So in fact we are losing 1% of our starting point. The solution equation doesn't take that into account and is completely disconnected from the starting point. (And no, the 1kg is not the connection b/c it has no relative connection to the total balance). Imagine you have 99 yellow balls and 1 red ball. And after some picks you end up with 1% less yellow balls than you started with. How many balls are then there in total? It will most likely not be 50 balls. The problem is the re-phrasing of that task, saying after some picks I'll end up with a 1 red ball and an amount of yellow balls that will give me a 98% portion of yellow balls, over all balls.

[@litcrit1624]

I always did this one in my head. Originally the dry melon 1 kg was 1% of the whole; now that same 1 kg is 2% of the whole. So how much do you have to multiply that 2% to get up to 100%? 50. I have a feeling it would've been harder if the number is weren't so easy to keep in your head.

[@NichaelCramer]

I’m glad you included the final, more “visual” solution. It’ll help, for example, in “dinner-table discussions” where I might want to explain this interesting example to folks who aren’t interested in (or who might not follow) “all that algebra stuff”.

[@JLvatron]

I got this right, but at 3:58 it is an assumption that the solid mass remained as this was never made clear in the question.

[@camelopardalis84]

@@JLvatron You are right. It is only implied.

[@camelopardalis84]

You are right. It was only implued, which is indeed not clear enough.

[@bjorneriksson2404]

Well, the "dry mass" can't exactly evaporate, so that mass remaining the same is an obvious deduction to make. Not everything should have to be "proven" in problems like this, because then you can start to demand proof of the fact that 50 is indeed half of 100 instead of just assuming that it is.

[@TheEulerID]

Correct, and I have made the same observation, and it seems that, in addition to water, melons contain over 100 different volatile compounds.

[@ModelLights]

@@bjorneriksson2404 ' "dry mass" can't exactly evaporate' Dry mass can't evaporate, and taking out 1% from the water weight doesn't make water magically drop to 50 kg from 99 kg. You guys realize at the 4:30 mark where the math is taking the ALREADY REDUCED TOTAL WEIGHT of 99 kg and multiplying it by '98%' which is NOT THE WATER REDUCTION FACTOR to get the 'paradox' is bad math, not a paradox, right? OF COURSE it reduced it too far, that 98% is self references 100%, not 'only the water weight reduction starting at 99%'. This is brain rot, I highly suspect the whole 'bunch of PhD's all arrived at this same answer after being told it was wrong' is completely made up garbage. If it was 100% water weight, and it reduced a percentage to 99% water weight, it would be 99 kg, it would NOT magically jump down to 50 kg from a 1% reduction. This is ONLY THROWN OFF A TINY BIT by 1 kg of the 100 being solid and not reducing by its 1% as well.

[@yurenchu]

From the thumbnail: 50 kg. Due to the drying out, [99 kg water + 1 kg non-water] changes into [49 kg water + 1 kg non-water] , so the water content changes from 99% to 98% . 10 minutes of explanation? Okay, let's watch.

[@oneyearunder]

I'm glad that I got this one right, my logical was, the 1% of the dry watermelon can't physically change, so something else had to have changed. If the unchanged value doubled then the water had to have halved

[@simonliljeqvist]

Interesting to me is that removing more than half of the water (50/99) only decreases the water content by 1% units Edit: I meant concentration or ratio instead of content

[@elSethro]

Looking at it the other way: "NOT water" has DOUBLED from 1% to 2%. This is a huge change. Since "NOT water" it is a constant (1kg both before and after), then water weight must have halved to produce that change.

[@themyief2406]

you are wrong here, the 99% was in terms of the starting weight but the 98% was in terms of the final weight.

[@leif1075]

​@@themyief2406yeaisnt the accurate way to say it you reduced the water content by 1 percent. Yea that's right. Because it dropped from 99.percent to 98 oercent water..so it's loterally correct to say the water content dropped by 1 percent..not sure where he got 50/99 from.

[@frankieking1941]

Thank you for your coment, now I understand……..I think😅

[@themyief2406]

@@leif1075 Ok, I had a hard time understanding your comment as it has improper grammer, but I think what you meant by your comment was "It is alright to say that the water content dropped from 99% to 98%". But that would be incomplete, as it should be, "the water content dropped from 99% of starting weight to 98% of final weight". Edit: Also it is incorrect to say that the water content dropped by 1% as the basis of measurement (i-e starting weight and final weight) are not same.

[@derekstanyer]

Usually even if I don’t get these I understand the answer pretty quick, but this took until the example with the dots before it made sense.

[@tench745]

The thought that illustrated to me just how much weight it would lose is realizing that 50% water content would weigh only 2kg.

[@abcd123906]

The most intuitive way to think about it is that, firstly, we know the dry weight must stay the same throughout. And yet, the percentage of the dry weight DOUBLED, from 1% to 2% of the total weight. So if the dry weight percentage DOUBLES while its absolute amount remains the same, the ONLY way that could happen is if the total weight HALVES.

[@adamrussell658]

Did the math. Surprising answer. Had to check if it was right.

[@Prs722]

With the watermelon/potato problem, here's the way I visualize it. So it goes from 99% water by weight to 98% water by weight. This doesn't mean much so it's better to say it goes from 1% solids by weight to 2% solids by weight. The percentage doubles, but we don't magically end up twice as much solids, this means half the weight must have gone.

[@furbyfubar]

It baffles how/why someone could think substituting watermelons with potatoes would make sense. What type of potato would have its water content be 99%? Google tells me that raw potatoes contain ~79% water, and cooking them only brings that number down. But because this riddle/paradox is mentioned so many times online, google suggest questions like "Are potatoes 99% water?" and then give the "suggested answer" from a page rephrasing this riddle.

[@yasseindahshan3556]

I did this considering water contenet as moisture content which is (total mass of water/total mass of other) instead of (total mass of water/ total mass). Which made my answer ~=99.497487.

[@abhishankpaul]

IMO, this is more of a wording issue than mathematical

[@Peter_1986]

I tend to be more of a visual learner when it comes to these kinds of puzzles, so the visual method at 9:15 made a lot of sense to me.

[@ambhaiji]

0:10 I think an attempt was made to do the 'in the beninging' meme and then decide halfway to follow a civilized scientific discourse.

[@g.mitchell7110]

I knew the answer right away, and not because I saw the same problem on Vsauce2 (The Potato Paradox). That video is about potatoes and this one is about watermelons. These are different types of food altogether.

[@tolkienfan1972]

Lol

[@emurphy42]

Sorry, I only know how to solve this for oranges.

[@dirkbester9050]

True, you can just plant the potatoes and hope for better luck next year. The watermelon in the picture are seedless, so no such luck.

[@BigNWide]

There is an assumption made in the answer that the 99% or 98% water is percent by *weight*; but it is also possible to interpret this part of the question as 99% or 98% by *volume*, in which case there is not enough information to solve the problem. Whenever you are given a percentage, the first question to be answered is "percent of *what*?"

[@DhoklaAboveVadapav]

My boy Presh was blabbing for full 10 mins but your 4 liner comment made me understand in less than 30 secs. Thank you.

[@BradHouser]

It is also interesting to note that if you want to dilute a liquid that is already 98% water, you would have to more than double (increase by 50/49) the water content to reach 99%.

[@g.h.190]

So many comments suggesting question is badly worded. To me it sounds like they are trying to invent an excuse for their failed answer.

[@MaulikParmar210]

English across world is pronounced and written differently, people will get it wrong even if relative grammar is correct. Comprehensive skills do not work when question is deliberately worded to create confusion and change meaning which could be expressed with more words. Welcome to languages 101.

[@ciaucia156]

Is the part of my soul is doubled from 1% to 2% in my potato body? That is the question today :)

[@CW91]

After looking at your dots visualization at 9:10 actually, the answer is the watermelons stay the same weight. Because before the water was dried up, 99/100 water and 1/100 dry weight cannot be simplified anymore so that is the weight. But after the 1% water dried up, so we have 98/100 water which simplify to 49/50, and 2/100 dry weight is simplified to 1/50. Even though we have simplified the fraction to 49/50 + 1/50, this doesn't mean that the weight of the watermelon becomes 50kg. It simply means (49/50) * 100kg is water and (1/50) * 100kg is dry weight. So if we assume any water which is loss has been converted to dry weight, therefore there is no loss of weight at all. (If we assume that there is no conversion, then we need to know how much of the dry mass is left behind after the water decreased for that part of the fruit) This question is incomplete about mentioning how much does the dry weight actually weighs. ------------------------------------------------------- Ok after a little clearing up of confusion, I understand what the water and dry mass means. So water is only water without any sort of mass in it, which means that after it dried, there is no leftover mass for that part. And dry mass means that the fruit mass, which even includes those parts mixed in water. So now we know that 100kg of fruit with 99% of water and 1% of dry mass means that the 1kg of dry mass doesn't go anywhere. A completely dry fruit (after 100% water is dropped) still has 1kg of dry mass. So the calculations are correct as in the video: 98% water and 2% dry mass means that the 1kg is equal to 2%. Therefore 98% (which is 49 x 2%) is simply 49 * 1kg so it is 49 kg. The reason why the answer has an extreme drop of water mass is because the 1kg dry mass did not change in proportion to the 1% drop of water percentage. Thanks @jensraab2902 for clarifying😄

[@jensraab2902]

It doesn't say that 1% of the water dries up, it says that the water content drops to 98%. The assumption that this is the case when 1% of the water evaporates is the very thing Presh tries to demonstrate to be false.

[@dirkbester9050]

Evaporation to a gas does not "make the water dry mass".

[@jensraab2902]

@@dirkbester9050 I think you fundamentally misunderstand the problem. Nobody suggests that water converts into dry mass, that is ridiculous. When the problem says that the water content drops to 98%, it means that the water content decreases to such an extent that the dry mass, which remains unchanged!, now accounts for 2% of the watermelon. It is exactly this fact, which is that the dry mass does *not* change, that is the key to solving the problem. Previously, 1% of 100 kg was dry mass, i.e. 1 kg, with the other 99 kg being water. After water has evaporated (not converted!), the 1 kg is not 1% by 2% of the entire mass. For this to be the case, the entire mass needs to have decreased to 50 kg (because 1kg/50kg = 0.02). With 1 kg being dry mass, the remaining 49 kg is water. So 50 kg (99 kg - 49 kg) must have evaporated.

[@CW91]

@@jensraab2902 bro you are playing with words. Water does not dry up, but water drops, drops where? It is the same meaning of decreasing the water... Also 1/50 is simplified fraction of 2/100 which I have said 100kg is the original weight of the watermelon, so we cannot simplify it to 50kg... Anyway my last sentence in my comment is that we are not given information about dry mass, so this causes much confusion and uncertainty. Also imagine if the question says 100% of water decreased, does this mean that the fruit has no more weight? There is still dry mass remain after all water drops right?

[@jensraab2902]

@@CW91 I don't want to be rude (and hopefully will not sound rude) but there really is not uncertainty here. It seems to me that you, respectfully, somehow have difficulties decoding the wording of the mathematical problem (perhaps due to a language barrier?). It is of course the melon that dries up, not the water; it is the water _content_ that drops, not the water (it is the figure that drops, decreases, gets smaller, not physical water dropping like a drop of water). Anyway, you say that we don't have information about the dry mass but we do! I even made the quick calculation at the beginning of the third paragraph of my previous comment. The watermelons have a mass of 100 kg, right? We are told that 99% of these 100 kg is water (that's what 99% water content means). The other 1% is the dry mass. 1% of 100 kg is 1 kg. You ask what would happen if 100% of water decreased. "Does this mean that the fruit has no more weight?" - No, of course not. Unless the entire fruit consisted of water (which will not be true for any real fruit), there will be some rest left, the dry mass. "There is still dry mass remaining after all the water drops, right?" Yes, exactly. In the example at hand, this dry mass would remain at 1 kg. In fact, the dry mass of 1 kg never changes in our scenario, it is at 1 kg at all times. I hope this helped to clarify the situation a little! 🙂

[@Catman_007]

Simple solution.. Solid portion of watermelon will be constant. So Solid portion = Total weight x Solid portion % So we can say that total weight and solid portion % is inversely proportional to each other. As we can see percentage of solid portion changes from 1% to 2% So weight changes from 2 to 1.. Hence from 100 to 50

[@feelshowdy]

I solved it by solely considering the dry weight, since it is a fixed value. Both in the beginning and end, we have 1kg of dry weight. However, this same dry weight which accounted for 1% of the initial weight now accounts for 2% of the final weight. If 1kg is 2% of the final weight, then I multiply that by 50 to get 100%, which equals 50kg.

[@GetMeThere1]

It's interesting that it would have been easier intuitively if you said the final percentage was 90%. One would say "well, if the dry weight was originally 1, and it's still 1, then the water would be 9, to make it 90%." And so it would weight 10 lbs. After a bit of head scratching, then, yeah, 10 lbs.

[@yippee8570]

10lb = 4.5kg, so nope

[@LeviATallaksen]

I think the main confusion is that the phrasing of the question makes it sound like it's all about the amount of water, with % being the unit for measuring it. Which is creating trouble because the unit is also changing. For the record, my first thought was also 99kg, but I realized the mistake very fast (like many others, I assume)

[@GuanoLad]

I didn't understand your answer at all until you mentioned the dry weight as being 2%. Then I saw it was about proportions, not about how much water was lost.

[@cguy96]

My intuition was around 50%, but I was surprised it was an integer answer.

[@ShawnF6FHellcat]

I got it right by using a weird version of the final method: You have 100 equally weighted units, where 99 are water and 1 is melon. The ratio is 99:1. Afterwards you have 98 units water and 2 units melon. This is a 98:2 ratio. In order to make the ratios compatible, I simplified 98:2 to 49:1. This means that there are a total of 49 + 1 aka 50 of the original 100 equally weighted units remaining. Since 1 unit was originality 1% of 100kg, we know that 1 unit = 1kg. Multiply 50 units by 1kg and you get 50kg final weight. This went much quicker and simpler in my head.

[@andreketaren]

I checked the truck's cctv and saw some burglars stole half of the watermelons

[@yackawaytube]

It's called level-1 thinking vs level-2 thinking. Try this one. The combined price of 2 items is $1.10, first item is $1 more expensive than the second item, what are the prices of the 2 items. Level 1 thinking gives $1 and 10c, level 2 thinking gives $1.05 and 5c.

[@RomanQrr]

I remember when I first encountered this puzzle I also thought it was 99 kg. A really great problem to poke holes in our intuitive understanding of reality.

[@michaelmetcalfe639]

I saw this and the first thing I realized is that there are 2 parts to the problem the water weight and the solid weight. Since there are 2 parts we have to check the answer against both parts and make sure there are no contradictions. So I tackled the water part first got the wrong answer but then compared it to the solid weight side. Realized it made no sense and why and then came to the correct answer. I can see this tripping a lot of people up because the question focuses so much on just the water side of the problem that people will miss the other side of the problem.

[@LaukkuPaukku]

At first the non-water weight is 1/100 (100%-99%=1%) of the total, then 1/50 (100%-98%=2%) of the total. Just multiply the non-water weight (which remains constant) by the inverse of the fraction to get the total.

[@Neodynium.the_permanent_magnet]

Amazingly counter-intuitive!

[@Tiqerboy]

I remember a similar quandary when we were all seriously concerned about low fat diets. So you had 2% vs 4% milk, and it was easy to say it doesn't matter because the 4% milk only has 2% more fat than the 2% when in fact it has twice as much fat, or put another way, 100% more fat.

[@IvanToshkov]

This is one of the reasons I'm always suspicious around percentages. They can be quite counter-intuitive. And the press *loves* to use them all the time.

[@jespado]

I solved it in my head in 30 seconds. I must be a genius!

[@metroid031993]

The way I did this (and got the correct answer, knowing it was going to be tricky) was that initially, 1 kg was 1%. After the weight reduction, 1kg was now 2%. In order to get 100%, you need to multiply that 2% by 50, and since 2% is 1 kg, 1 kg * 50 == 50kg for 100%

[@Able89535]

The terms “Absurd” or “counter-intuitive” are subjective, highly depends on your knowledge and your mindset (how you view the problem at first sight). Hence the term “Veridical paradox” is also subjective and some can think that it is, while others may think it’s not.

[@joe_z]

The first time I saw this problem, I thought 99 kg like everyone else, but then I checked that answer in my head and realized that the water concentration was still really close to 99%. Then I worked backwards like in this video and got the true answer, and was extremely surprised at how the math checked out.

[@gaijininja]

It's questions like this is why I don't answer the math questions on Facebook any more. They are all designed to have an easy to spot logical but wrong answer, and a more difficult rule following answer that seems wrong, even when shown visually.

[@jackalovski1]

this is a similar problem to what I had when I first went into business with my brast friend. at the time he was selling products on ebay which charged 20% fees, because he was a top seller he got a 10% discount on those fees. he was also VAT registered which meant that 20% of the final sale value was paid to the government. he coulondt work out why he was making a loss on the things he was selling, turns out he made a bunch of mistakes. he thought the selling fees were 10% but it was a 10% discount on the 20% so the total was 18%. The other mistake he made was that the selling fees AND the VAT were charged on the final sale value which included the material costs, the manufacturing costs, the shipping costs and the flat paypal charge of 20p. He was calculating the sale cost based on the sum of the costs multiplied by 30% (20% VAT plus 10% fees). which gave the wrong price.

[@stevethorpe]

I don't consider myself particularly good at maths, but my mind went straight to: "From the initial condition it is obvious that the non-water weight is 1kg. In the end that 1kg is 2% of the total weight, so the total weight must be 50kg. I guess that is similar to the 'dots' method, but without the dots 🙂

[@Magst3r1]

I realised the non-water part should double, but then didn't think any further and just guessed 99.5 kg for some reason lol. Instantly realised it when he said 50 kg

[@Chill-Ice]

Me in the first 10 seconds: Wait, how do you carry watermelons by train?

[@Doeniz1]

I thought there was some trick involved and was pretty disappointed, when the solution turned out to be just the straight foreward approach.

[@anuragguptamr.i.i.t.2329]

I am really very glad to see my Alma Mater's (IISc) one of the questions at this channel. 😍💥

[@chrilaur1143]

I approached this by considering the difference in start weight (Xs) and end weight (Xe). Since the weight of melon solid doesn’t change, Xs-Xe=Ws-We, where Ws and We are the weights of water. We know Ws=0.99Xs and We=0.98Xe. Substitute in and rearrange to get 0.01Xs=0.02Xe. So Xe=1/2Xs=50kg.

[@DerangedAussieMan]

The way I solved it was to look at the "dry weight". Watermelon is 1% dry weight and the total weight is 100kg. Now we get rid of some water so the dry weight is now 2% of the total weight. Since the dry weight doubled proportionally, then the total weight must've halved, so it must be 50kg now.

[@0ur_6_stars]

So if water at last is *98%* , that means dry weight is *2%* . We know that dried weight is 1kg . Let the final weight be *w* . So , 2% of w = 1kg i.e., 2/100×w=1 W= 1×100\2 Which gives us *w=50kg*

[@redplanetzeal1461]

To be fair, the question does not mention that the dry weight remains the same during the journey, so we can come up with any numbers for the answer, as long as the water content is 98%.

[@MrNostril]

I would have got this wrong if it wasn't a mind your decisions video. But I knew he wouldn't be presenting it if it was an intuitive answer. So, I got out a pen and paper and worked it out. Simple, to calculate, but not solved the way you initially intuit.

[@lakshya2132]

U could have taken the mass of watermelon to be constant and 1%of 100kg = 2% of end weight of watermelon (as 98% was water and the remains 2% was constant)

[@robertveith6383]

* *You*

[@lakshya2132]

@@robertveith6383 U*

[@cobaltchromee7533]

My thought process was this: 1. Water is 99% of the weight, so the other things sum up to 1% 2. After evaporating, there's 2% of the other stuff. 3. That means that 50% of the water has evaporated. 4. The answer is 50 kg

[@charlesbromberick4247]

I´d believe the economists blew it, but not the scientists. A scientist underatands percentages and would reason as follows: starting out we have 99kg of water and 1kg of solid (which won´t change). At the end 98% is water and this means 2% is solid (which is 1kg). So 1kg is 2% of total weight which implies total weight must be 50kg. Thanks for the fun puzzle, Presh.

[@justingolden21]

It's an ambiguous question. It can be interpreted as 98/99 * 100 or as 100 / (100-98)

[@delanomighty8113]

This is one of the first things we do as chemical engineers. The key is to do the calculations on the amount that does not change - i.e., the 'dry' mass.

[@HotelPapa100]

My gut feeling that there would be a difference in the order of 1% because of precise vs. approximate math. I was quite baffled when I did the actual math. It was clear that I would have go via the dry mass.

[@knotwilg3596]

The fastest solution is focusing on the dry weight. At start it's 1%, by the end it's 2%. Its ratio has doubled, it's stable itself, hence the total weight has halved.

[@nicholasmakin7659]

The phrase, "'is' number over 'of' number equals percent number over 100" has served me well since high school: 1kg/x=2/100

[@SacoSilva]

My first job interview had a similar question but in terms of fish in a tank and the wording made it easier to get the right result (there are 99 red fish and 1 blue fish in a tank, how many fish of each color do you need to remove to get 98% red fish?) I managed to get it right and because of it I intuitively answered 50 to this one but weirdly enough I couldn’t do the math.

[@philliberatore4265]

From an engineering point of view, the dry weight (the meat) has a little effect on the total weight of the sample. It is mostly water, and the meat weight can be ignored. My approximation was half - 50 kg. Close enough.

[@tomdekler9280]

I have no idea how watermelon water loss works so I got tripped up on the idea that the 1kg of "other weight" should remain the same. Maybe if it was clearer in the original question that the water evaporates instead of, idk, some chemical reaction that adds the hydrogen and oxygen atoms to the dry weight.

[@Xenon.O]

You can't just assume that 99% of the watermelon's "content" is the same as 99% of its weight. I don't know why they keep making their questions' wording difficult to understand.

[@Bully_Maguire007]

I remember giving kvpy when I was in 11th What happened was we had registered in 2021 but the exam held next year (2022) due to some issues And that was the last time kvpy was conducted 😞

[@solandri69]

Stuff like this shows up in lots of places. Marketers for early OCR (optical character recognition) software would exploit this. They'd advertise their software as having 99.95% accuracy. You'd compare that to much more expensive software which advertised 99.99% accuracy, and think "0.04% difference is tiny, it's not worth the extra money." But It actually means if you get the cheaper software, you need to manually correct 5x as many errors. A similar thing happens except on a geometric scale. SSDs are commonly marketed in MB/s or GB/s. So you see a cheap SATA 3 SSD which hits 500 MB/s, vs a NVMe SSD which costs 50% more but can hit 2 GB/s. You think "50% more money for 4x the speed? Obviously get the NVMe SSD." But humans don't feel speed in MB/s. We feel it in how long we have to wait, or sec/MB. Say you need to read 100 MB of data. How long do you have to wait? The SATA SSD can do it in 0.2 sec. The NVMe SSD can do it in 0.05 sec. Can you honestly tell the difference between 0.2 sec and 0.05 sec? 99% of the time you can't. People have actually done this test, setting up identical systems with a SATA SSD and a more expensive NVMe SSD. And people can't tell which is which. The SATA SSD is "fast enough" for 99% of tasks. (It only begins bottlenecking you if you're working with extremely large files.) Then there's MPG for gas mileage. If you used to drive a 15 MPG SUV, and switch to a 30 MPG sedan, you save 2x the gas right? So if you'd switched from the 30 MPG sedan to a 60 MPG hybrid, you'd save 2x as much gas again, right? Not exactly. Say you go on a 60 mile trip. The SUV uses 4 gallons. The sedan uses 2 gallons. So as expected you'd cut your gas consumption in half. But if you'd used the hybrid isntead of the sedan, you'd only save 1 extra gallon, not 2 gal or 4 gal. Why? Because MPG isn't linear. A 1 MPG improvement at 15 MPG, saves a lot more fuel than a 1 MPG improvement at 30 MPG. So the 15 MPG improvement going from 15 => 30 MPG, represents 2x the fuel savings of the 30 MPG improvement going from 30 => 60 MPG. The vast majority of the fuel savings comes at improving lowe MPG vehicles, not improving high MPG vehicles. Because of this, we went down the rabbit hole of turning hybrids into econoboxes. The first vehicles we should have turned into hybrids were trucks and SUVs. The reason is MPG is the inverse of fuel consumption, so the higher MPG gets, the less difference increasing it makes. Because of this, the rest of the world uses liters per 100 km (equivalent to 1/MPG).

[@CashueTM]

Question phrasing should say water content was 99% *** of its mass ***

[@robertveith6383]

No, it should state "of its mass."

[@CashueTM]

@@robertveith6383yeah your right . I’ll edit the comment

[@jensraab2902]

Yes!!!! Full agreement. But in practice, I doubt that what is measured is mass. We usually measure weight and erroneously call it mass (or rather label the weight "kg" in error). I've never tried it but I suspect that if you weigh the same pack of, say, flour or sugar or whatever with ordinary scales at the poles or at the equator, the figure will be different but say "kg" when in reality it should be the weight in Newton. But then, the precision of these scales will probably not be good enough to measure that difference. Still, even though this is a math and not a physics puzzle, I think Presh should be more precise and use correct terminology. I'm sure he's aware of the difference.

[@SmileyEmoji42]

No. If it was %volume then it would be unsoivable because you'd have to know the density of watermelons. Any reasonable person, or anyone who's ever read almost any food ingredients label, will assume that it means % by weight (and only pedants will point to the distinction between weight and mass).

[@jensraab2902]

@@SmileyEmoji42 Did anybody talk about volume here? I don't think anyone did. As for the distinction between weight and mass, it may sound pedantic for ordinary people, but for folks with an affinity to physics (such as me) the difference is not at all trivial. I'm not Don Quixote, I won't be fighting against these windmills because I know it's a lost cause; I've accepted that in colloquial speech weight and mass is often used incorrectly. But in a place where people might not only be interested in math but also science, I think it's totally fine to remind people of the difference. People (and I don't exclude myself) sadly have so many misconceptions that there's no harm, in my opinion, to remind them from time to time of the actual facts. If nobody pointed out these misconceptions, how are any of us supposed to get rid of them?