Dave can cut the lawn in 50min, Ed can do it in 40min, how long will it take if they work together?

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[@tmacaulay]

In one minute, Dave cuts 1/50 of the lawn and Ed cuts 1/40 of the lawn. So after 1 minute, 1/50 +1/40 of the lawn is cut. 1/50 = 4/200. 1/40 = 5/200. So after 1 min 9/200 of the lawn is cut. 9/200 is to 1 minute as 200/200 is to x minutes. x=200/9 = 22.2222 minutes.

[@A5760S]

It´ll take them at least 55 minutes because they sit down, chat, have a beer together or two... and time goes by...

[@dianelewis7469]

lol

[@bsmb2017]

Now that is some reality

[@L17_8]

Jesus loves you ❤️

[@joscelynmiller9333]

31.6

[@johansteyn8526]

Yes LOL😅

[@dough9512]

But they only have one lawnmower!!

[@L17_8]

Jesus loves you ❤️

[@carlosspiceyweaner4995]

What a twist!

[@samsoile]

Since they are both landscaper, they should have their own lawnmowers. Of course this is an assumption I am making, but I think assuming they only have one lawnmower has a lower probability rate. What do you think?

[@panzerswineflu]

It's not stated they are landscapers. Could be brothers and the parents told them to cut the grass​@@samsoile

[@janelloyd3247]

LOL, from a math teacher!

[@fbj9648]

In 50 minutes if they work together they will cut 2.25 lawns. So time is 50 : 2.25 = 22.22 minutes

[@Daeananaias]

If they work together How much lawn would Dave actually do as opposed to Ed

[@KAF128]

Yes, that is the proper answer. I like it! But see also my 'cheat' above ! LOL!

[@r3jk8]

This is the easiest and simple and clearest answer.

[@r3jk8]

I solved it without using much math. If they each could do it in 50 minutes, then it would take them 25 minutes. If they each could do it in 40 minutes, then it would take 20 minutes. The answer lies in between. The answer is d.

[@KAF128]

Similar to me... see above !

[@mariekatherine5238]

Exactly! Did it mentally.

[@stevenflogerzi1955]

Another way to do this is if you only have 2 parameters is ... A x B divided by A + B

[@Bens963]

Way better than my answer, I did it the long, boring way, thanks a lot for the information

[@krwada]

It will take all afternoon, and perhaps a case of beer

[@dianelewis7469]

lol

[@L17_8]

Jesus loves you ❤️

[@lisbetsoda4874]

​@L17_8 leave religion out of it. It is just math, after all.

[@hansnagle5764]

Imagine they walk towards each other on a field of 100 yards of length and a width of one lawnmower. Now you can make the next equitation: 2t = 100 - 2,5t, so 4,5t = 100 and so t = 100/4,5 = 22.22… min. This is the moment they meet each other and the job is done.

[@robertloveless4938]

If there were 2 Daves, they could cut it in half the time (50min/2= 25min) Since Ed was faster than Dave, the time MUST be less than 25 min. ... Once again, when you're offered multiple choices, eliminate the impossible ones. ALSO - find the average time of the 2, (50+40)/2 =45, and cut it in half (45/2). Teachers must teach students to think BEFORE tackling the answer.

[@Onoelo23gf]

200/9=22.2 min.

[@gavindeane3670]

Your first approach is spot on and is a good thing for a teacher to discuss. Your second approach - calculating the average - only works as an approximation because Ed and Dave work at a similar rate. That would be a good one for a teacher to show how it doesn't work at all when Ed's and Dave's rates are very different.

[@Nclght]

22.2. I need to determine how much each can cut per minute. So, I created a yard size of 200 yds ( it doesn't matter the size but i used 200 as it's easily divided by 50 and 40 ie common denominator) For each minute, Dave cuts 4 yards, and Ed cuts 5 yds. Together, they cut 9yds per minute. So to cut 200 yds together, it will take 22.2 minutes.

[@tomtke7351]

D : rate of work of Dave E : rate of work of Ed D = lawn/50min E = lawn/40min D+E= lawn(1/50min+1/40min) = lawn((40+50)/(50×40)) = lawn(90/2000) = 90lawn/2000min = 9lawn/200min if the combined RATE OF WORK is 9/200 lawn/min then the question's answer is 200min/9lawn =22.2min/lawn

[@MIck-M]

It would be interesting/entertaining to then add to the problem with, 'They both then become complacent and Dave only mows at 2/3 the pace while Ed mows 5% slower than usual but also loses a further 6 minutes going to the fridge to get more beer' I am going to need a sharper pencil for this... and a beer 🍺 Silly yes, but real world stuff. Love these vids

[@dianelewis7469]

lol

[@johnhudelson2652]

Use simple logic: If each one of them can cut the lawn in 40 minutes, then the answer would be 20 minutes. If one takes 40 minutes and the other takes 50 minutes, then it will take slightly longer, so the likely answer is 22.2 minutes.

[@richardhole8429]

Right on! 50/50 is 25 minutes, 40/40 is 20 minutes. It must be near to half-way between 20 and 25 minutes.

[@normhardy]

That's the only logical solution.

[@39sj55]

22.2 minutes is to short

[@georgerichman8293]

Sure, but the solution can be applied to many other situations.

[@normhardy]

Make it a show your work problem. Rate×Time=Work (1/40+1/50)×Time=1 That's one way I taught this type of problem.

[@johansteyn8526]

22.2. Min. If they work together obviously it would take ½ of the time. Since Ed works faster his time will be the dominating factor. Common sense tells me it has to be 22.2 min without any calculations needed.

[@jstep17yt]

You have great content. I strongly suggest being quicker to the answer. It took you too long to get to the answer as well as the key elements to solve.

[@ellyza24]

Agreed!

[@nickfraser4599]

In one minute Ed can do 1/40th of the lawn. In one minute Dave can do 1/50th of the lawn. Assuming they start at opposite ends, In one minute they can do (1/50th + 1/40th) of the lawn or 90/2000ths of the lawn or 9/200 the of the lawn, but there is only one lawn. Thus it takes 200/9 minutes or 22-2/9ths minutes to do one lawn

[@egaydemesa5353]

1/50 + 1/40 = 1/x solve for X. X = 22.2 minutes. It will take 22.2 minutes to cut the lawn if the work together.

[@johnnyragadoo2414]

Fun to work through, but you didn't explain why the sum of reciprocals worked! Dave cuts lawns at a rate of one lawn per 50 minutes. Ed cuts one lawn per 40 minutes. Some number of minutes times Dave's minute rate plus Ed's minute rate equals one lawn. "Per" is a code word for divide. Dave's rate is 1/50 (one lawn per 50 minutes) and Ed's rate is 1/40. In one minute the two together cut 1/50 plus 1/40 lawns. In x minutes times (1/50 + 1/40), they will cut one lawn, or x(1/50 + 1/40) = 1. Divide each side by x to get 1/50 + 1/40 = 1/x minutes (your equation). 1/50 + 1/40 = 9/200 which equals 1/x. Cross multiply or just flip both sides upside down to get 200/9 = x, or 22 and 2/9ths minutes to cut one lawn. So, let's say Dave can cut 3.5 lawns in 135 minutes and Ed can cut 2 lawns in 68 minutes. How long for the two of them working together to cut 8.3 lawns? Easy, if you treat Dave and Ed's stats as speed and remember one lawn isn't a magic number. x(3.5/135 +2/68) = 8.3 x * 508/9180 = 8.3 Divide both sides by x for 508/9180 = 8.3/x. Divide both sides by 8.3 to get 508/76194 = 1/x. Flip both upside down to get 76194/508=x, so x equals 149.99 (roughly). Double checking: 149.99 times 3.5/135 + 149.99 times 2/68 equals 8.3. Of course, always watch your units. Algebra works on symbols, too. Lawns/minute times minutes equals lawns times minutes/minutes, or just lawns.

[@denisewenke8323]

True. I'm surprised this comment hasn't gotten a bunch of thumbs down from those complaining that the explanation is already too long, though 😂

[@johnnyragadoo2414]

@@denisewenke8323 Ha! Good one. My weakness, I love the sound of my keyboard rattling and I know I'm worse in person. My wife, the stories she could tell....

[@denisewenke8323]

@@johnnyragadoo2414 Oops! I meant the video explanation. Thanks for taking it graciously.

[@RyguyAB]

I prefer to think of work problems where they are both doing the same job in terms of percents and the time it takes each person to complete a certain percentage of the job. In this case one person completes 2.5 percent of the job in a minute (100 percent / 40 min) and the other completes 2 percent of the same job per minute (100 percent / 50 min), so together they can complete 4.5 percent per minute (2.5 + 2). Then, to figure out how long it takes them together, it is simply 100 percent divided by 4.5 percent per minute which gives you 22.22222 minutes. One of the reasons I like this approach is thatbl thinking of it in terms of the percent of the job thay each if them can do per minute is a reminder that they are working on the SAME job and each doing a part of it. It also reminds me that if the question is structured a bit differently that it has to be approached differently. For example, if the problem were worded such that one person could mow a 5000 Sq. Ft l. Lawn in 60 min and another could mow a 2500 sq. ft. lawn in 25 min and how long would it take them to mow a 4000 Sq.l ft lawn together, I would know that I would have to figure this out in terms of Sq. Ft per minute first for each person and then using the total size of the combined job instead of percentages.

[@wowplayer7986]

I chose correctly!! My viewpoint was...if there were 2 Dave's it would take 25 minutes and if it was 2 Ed's would take 20 minutes and then took the average.

[@arolimarcellinus8541]

Please explain that formula. I never found such formula, usually only used it in resistor parallel equation

[@tominmo8865]

Without doing any significant math you can figure out which answer is correct, for a multiple-choice test. The two guys average 45 minutes each to mow the lawn, so together they would mow it in 22.5 minutes. Takes about two seconds to do this. Not perfectly accurate, but plenty close enough.

[@andyparal]

It took several months, because they bumped over a family of moles, killed them and the lawnmowers in the process, went to prison for killing the moles and then, after being released, they had to order new lawnmowers, as nobody was capable of repairing them. See, that was easy to solve and without using any math skills at all. 😉

[@SSrivastava-mu1ke]

Absolutely true I can certify. That is how it went. True ! ... and when they took a break they started looking at this video and since men of work don't quite jell with men who do real work, they are still watching and since they are still watching , naturally the lawn moving is still incomplete and to me this looks like a black hole, the video cannot proceed forward and hence they cannot complete the work . 😮

[@AllanFlamm]

what happens if you divide the lawn in half, the 1st guy cuts in in 25 minutes the other will take 20 minutes both take 45 minutes in total

[@charlesmitchell5841]

I actually learned something today with that work formula. Nice! 👍

[@ingridlarssen7483]

I LEARNT HOW BAD THIS AMBIGUOUS MATH TEACHER IS⁉️😂

[@lisbetsoda4874]

​he is making sure everyone can follow. Don't put it down. That's pretty smug. @ingridlarssen7483

[@wiztub]

This assumes there are 2 lawn mowers

[@ingridlarssen7483]

YUP⁉️ BAD MATH TEACHER EXPECTS ONLY HIS MIND READERS TO ANSWER 🤔 HIS OWN PERSONAL LOGIC ⁉️😂 AMBIGUOUS MATH TEACHER = BAD = NOT THOROUGH AND EXACTING = HE FORGOT TO USE HIS LOGIC AND IF SOLVING WHETHER 1 OR 2 LAWN MOWERS WERE USED, THEN MORE INFORMATION IS NEEDED⁉️🏨😂

[@lisbetsoda4874]

😂

[@marthacalkins8054]

Over 50 years ago, I was ALMOST a math major. It probably would have been a mistake, but so was the major I ended up choosing. C’est la vie. Anyway, here I am, retired, and really enjoying these reviews; pleased at what I remember and what still comes easy, enjoying the brushing up of some of the stuff that I’ve gotten shaky on, and, frankly, enjoying the fact that I don’t need to feel any real pressure to know the really advanced stuff: I can come back to it and pick it up later, if I feel like it, but…hey, I’m retired!

[@Vipre-]

Being multiple choice makes it too easy. If Dave can cut the whole thing in 50 minutes then he can cut half in 25 minutes meaning the answer at most can only be 25, and since only one answer is 25 or lower it's automatically d, 22.2

[@dangermouse8466]

Hi there! Thank you so much for the videos. I got the answer correct but used logic to get it right. What I'm not understanding is why we use this particular formula to get the answer? Can you tell us more about this particular formula and how it came to be? Are there any other formulas that can get to the correct answer? Many thanks.

[@Ayelmar]

Solved at the thumbnail, the answer is d)22.2 min. In fact, of the 4 options, that's the only one that even REMOTELY makes sense. Working together, they could cut TWO yards in 45 minutes ( (50 + 40) / 2 = 45), so cutting just one would take half of that time.

[@suerowe53]

Exactly! Worked out at a glance without the multiple answers and all the algebra cr*p... it's common sense 😊

[@neilmccoy9390]

The answer is proportional to the sum of the reciprocals of the times. Let's see how many lawns can be mowed in one hour. Dave can cut 60/50=1.2 lawns per hour. Ed can cut 60/40=1.5 lawns per hour. So together Dave & Ed can cut 1.2+1.5=2.7 lawns per hour. Thus Dave & Ed can cut the one lawn in 1/2.7 hours which is 60/2.7=22.2 minutes.

[@aliso-pv7ll]

Use product over sum, as used in electronics.

[@minneapolisfoxden528]

if they both were at the slower 50 min rate, then together would be 25, but ed is slightly faster so must be faster than 25

[@GetMeThere1]

The choices A-D are unrealistic. Either one can cut the lawn in LESS than a hour, so if they work together, each can cut HALF the lawn in LESS than half an hour -- meaning choice D HAS to be right -- no calculations necessary.

[@KAF128]

I haven't seen the full 13 min clip or read many comments (I will, though!), but given the 4 possible answers, it is fairly trivial to eliminate 3 of them in a few seconds and get the answer with a bit of logic and MINIMAL maths - sorry ! If I assume for a moment, that I have 2 chaps who can each do the job in 50mins (and I know that Ed is actually better than that !) I can clearly see it would take them exactly half of 50 mins, or 25, If I then recall that having Ed on board reduces that time a little, there is only one option that is less than 25 mins. Simple... less than half a minute, from Keith, I mean.

[@robertwoolley8632]

Well, 2 people working at the slowest pace would take 25 mins. And 2 at the fastest 20. So as there was only 1 choice between 20 and 25. It was D, 22.2 and i didnt need to use algebra. All assuming there were 2 mowers availible

[@aku7598]

Let 1 unit energy required to do the job(physics) Bob power is 1/50 energy/min. Ed power 1/40 enery/min Work together total power = (1/40 +1/50) (1/40 +1/50)t =1 t=2000/90=22.2 min

[@Bens963]

Lets grab the rate first D = 1/50 E = 1/40 Combined rate = 40/2000 + 50/2000 = 90 /2000 = 9/200 lawn per minute. Now we'll need to divide the lawn by our new combined rate so 1 ÷ (9/200) = 1 * 200/9 = 200/9 = 22.2 minutes, final answer 👀

[@yvessioui2716]

It's an MCQ question, special approach might often do the trick like in this case. 1st, let say they both take 50 inutes to do the lawn; together they will take 25; thus eliminating a, b and c : leaving d as the correct answer. 2nd, kind of a confirmation, since the previous step, but Ed is even working faster than 50 minutes the answer should be less than that 25 minutes... so 22,2 looks pretty good. No complicated calculations and since no development is needed, checking answer is fast and furious. As teachers we must prepare our students for life on all aspects. MCQ questions can be solved in much more ways than the most tedious way. Good incentive to get the full calculations, give some topics where that kind of organization (sum of inverses equal inverse of searched answer) here like in electricity with resistances, in biology and sociology to estimte the existence and / or need in cooperation...

[@jonnamechange6854]

It depends on lawnmower availability. If there was only one available then they could share the work and b) looks correct at 45 min But if they both were pragmatic and wanted the job done more quickly, Dave could leave it to Ed to do it in 40 min, perhaps get him a cold beer. If there were two (equally performing) mowers available, and they could work together without getting in each others way, they could get the job done in 200/9 minutes. Maybe faster, because of the rate of grass growing not hindering them for as long. We should also consider whether both Ed and Dave could operate more lawnmowers, perhaps each lashing two mowers together side by side. This could potentially halve the time again, though I doubt it since the task would be too exhausting would slow down the walking pace. It's like some mowers power themselves along without pushing, but others need shoving along. We don't know enough about the lawnmowers. I would actually find it interesting to know what would happen if I lashed a powered mower next to a non powered one, if it would have enough grunt to move them both along?

[@majorpentatonic2310]

22.2 or 20mins if Ed whips Dave into shape 😂

[@denisewenke8323]

Ah, the spirit of competition. 😂

[@devildog4805]

Assume a unit lawn; area is 1. In 20 minutes Ed does 0.50 of lawn. How much lawn does Dave complete in 20 minutes? Ed's time/Dave's time = 20/25 = 4/5. 4/5 * 0.50 = 0.40. Lawn is 0.9 complete in those 20 minutes (0.5 + 0.4). 20 minutes / 0.9 = 22.222... minutes.Break time! Dave picks up a book on abstract algebra, Ed picks up a coloring book.

[@richardhole8429]

It is the same calculation as a 50 ohm and 40 ohm resistor in parallel! 1/Rt = 1/50 + 1/40

[@Jeff-xy7fv]

Or 50 microfarad and 40 microfarad capacitors in series

[@richardhole8429]

@@Jeff-xy7fv the formula is quite versatile.

[@johndoe3092]

harmonic average

[@hansnagle5764]

Nice solution.

[@Nclght]

Fantastic! But affecting these circuits (remember guys , it's parallel circuits not parallel circuit), there's an inductor slowing things down a bit...ie the inducement created each time they pass by that six pack of cold beer. 😂

[@chrischiesa609]

Let X be the amount of grass total. Dave cuts at X/50 per minute and Ed cuts at X/40 per minute. When working together they cut at ( (X/50) + (X/40) ) per minute, which simplifies to 9X/200 per minute. X amount of grass at this rate will thus take 200/9 minutes, = 22.2.. . (repeating) minutes.

[@JC-rn5tk]

Using an arbitrary 1000 sg ft lawn, Dave cuts at 20 sq ft per minute, Ed at 25. Add these two, then 1000/45 = 22.2. Alternately, the answer could be 36.6 minutes. Ed is overconfident in the time it will take working together and doesn't put enough gas in his mower. He runs out well before finishing and heads back to the garage to refuel. Dave meanwhile, is distracted while laughing at Ed and runs over a croquet ball that was hidden in the tall grass, stalling his mower and permanently damaging the blade. Ed finishes the job by himself after refueling.

[@mightyhero]

Daves rate: D x 50 = 1, so D = 1/50 Ed's rate: E x 40 = 1, so E = 1/40 Dave and Ed work together: (D x time) + (E x time) = 1 (D + E) x time = 1 (1/50 + 1/40) x time = 1 (4/200 + 5/200) x time =1 (9/200) x time = 1 time = 200/9 time = 22.2

[@dlkline27]

I admit total ignorance of solving this type of problem. Thanks for this lesson. Now all I have to do is remember the process. 😁😁😁😁😁

[@denisewenke8323]

Quick estimate, take the average and divide by 2 again, since they're each mowing about half of the lawn.

[@deltalima6703]

1)theres only 1 lawn mower, using math: 45 min 2)magic just using math: 22.5 min as both simultaneously mow seemlessly somehow. 3)realistic: 55min plus, as they visit and bugger around

[@gavindeane3670]

If there's only one mower then they can do it in 40 minutes. No need to get Dave doing any of the work. Quickest is for Ed to do it all. If they have a mower each and both mow simultaneously, it takes less than 22.5 minutes. It takes 22.222222222222222 minutes (infinitely recurring 2s after the decimal point, because it's 22 and two ninths minutes).

[@mauriziograndi1750]

Dave and Ed together have a potential cutting of 90 minutes. 100/90 = 1.111 As there are 2 people involved: 1.111 x 2 = 2.222 and as this is a ratios and we talking minutes then is 22.2 minutes.

[@terry_willis]

The 4 choices forced the correct answer d) by simple approximation. a) and b) are obviously silly.

[@harrymatabal8448]

Dave has already mowed the lawn so Ed can sit in the john

[@devonwilson5776]

Greetings. The correct answer is 22.2 minutes. Working together, it should be (1/50+1/40)= 90/2000 minutes. Now this should equal the time taken together. If we assume that the time taken is represented by X, then working together it should take 1/X minutes. Therefore, for the value of X, the time taken working together, 90/2000=1/X. That is 90X=2000. Dividing throughout by 90 gives X =22.22 minutes.

[@ajsaus4825]

22.2

[@overlordchungus2882]

Dave gets 2% done in 1 min. Ed gets 2.5% done in 1 min. Together they get 4.5% done in 1minute. 100% / 4.5% = 22.22

[@marye2815]

I did it in my head, using common sense and my answer was d. I actually came up with 22.3. I didn’t use algebra. The times you gave and the two working together it would take them 22 minutes and 30 seconds.

[@gavindeane3670]

It's 22 minutes 13⅓ seconds.

[@rodneyallen2672]

way way back in my noodle was a principle discussed in an intro to business class the talked about the Peter principle which stated that two people can do three times the work of 1

[@billfitzpatrick6202]

I thought the peter principle is that ppl will usually get promoted until they settle into a position where they ultimately are failures!

[@gaddy512]

Law of compensating errors. 2 Daves = 25 min. 2 Eds = 20 Min. answer in between 22.2

[@robertdworsky4104]

i would like you to explain why you are using this math method, if they each have a lawnmower.

[@KiloFeenix]

22.2, process of elimination, if it takes dude to mow half in 20 min and the other guy would need 25 then there would be a little more than half for the faster guy and a like less for the slower

[@aartbroekhuizen2375]

If there are 2 lawnmowers and both cut the grass, they can cut the lawn in 22.22 minutes.

[@brianmac1]

I didn't even need to work it out. If the slower guy Dave can do half in 25 mins, and Ed is faster so he'll do a bit more than half, the answer must be less than 25 mins.

[@t6v5c2]

Isn’t this basically a distance-rate-time problem solving for time? In other words, the “distance” is the lawn (1), the time for Dave is 50 and 40 for Ed? Asked another way, if Dave starts at one end of the lawn and Ed at the other, how long does it take for them to meet, i.e. finish mowing? 🤷‍♂️

[@user-sn9qf7wp8w]

Who said they only have one lawnmower? How do you know that?

[@T1Jafo]

It seems like Video takes longer to watch than Ed cutting the grass. However, if played at 2 x speed, not so bad.

[@deltalima6703]

I assumed it was a spherical mower. Took a long time.

[@kennethwright870]

If both at 40: 20 mins If both at 50: 25 mins So somewhere between. Only choice is d

[@treeblindbuck3260]

50 min. Because Ed is tired of busting his ass while Dave takes 3 coffee and smoke breaks, so Ed is tapping out and letting Dave do all the work for a change.

[@cyruschang1904]

lawn ÷ (lawn/50 min + lawn/40 min) = lawn ÷ (9 lawn/200 min) = (200/9) min = (22 + 2/9) min

[@mariekatherine5238]

Made an easy question into a much too complicated problem!

[@ebanavorio]

L'unica risposta possibile era la D, anche solo considerando che il più rapido finisce la sua metà in 20 minuti e poi aiuta l'altro a finire. La domanda sarebbe stata più difficile se mi avessero chiesto di calcolare direttamente il tempo del lavoro complessivo di entrambi.

[@JohnnyJohns-eb9qb]

It took one hour and fifty-six minutes because Dave kept getting in the damn way.

[@dianelewis7469]

lol

[@stevekerr2845]

Could have mowed the lawn during the explanation

[@iceman1231]

I had the formula like this ((1/2 x 50) + (1/2 x 40)) / 2 = 22.5 . Why is this incorrect.

[@gavindeane3670]

That is the answer to the question "what is the average of the time it takes Dave to mow half a lawn and the time it takes Ed to mow half a lawn?" The answer isn't going to have anything to do with how long it takes either of them to mow half a lawn, because that's not how much either of them is going to mow. It might be easier to see the why your calculation isn't relevant if we consider a more extreme example. Imagine Ed can mow a lawn in 100 seconds and Dave takes 100 days. Plugging those numbers into your calculation gives 25 days and 25 seconds. But that's not how long it's going to take them at all. They're going to set off, and after not quite 100 seconds Dave will have cut about 3 blades of grass and Ed will have done the rest of it.

[@wesleycreekmore7194]

Well its not a or b because it is not going to take longer so it its either c or d.

[@issadad]

In all fairness a splendid channel, but so prolonged and padded I just want to throw myself down a well every time.

[@christopherhinds9526]

what is the lcd

[@b213videoz]

Work = Dave's working minute * 50 = Ed's working minute * 40 Dave's working minute = Work / 50 Ed's working minute = Work / 40 [D's Wrk per 1 min E's Wrk in 1 mins] [---------------------- + -------------------- ] * X mins = Work [ 50 40 ] 4 * W + 5 * W ------------------- * X = Work 200 X(4Work + 5Work) = 200 * Work X*9 = 200 X = 200/9 = 22.2 = answer d)

[@Geoff_G]

At least an hour because when they get together, they goof off.

[@MrSummitville]

Beer!

[@dianelewis7469]

i guessed 22.2 of the choices closet to my answer 22.5

[@DroneLearner]

If they each cut half of the lawn then Dave takes 25 min whilst Ed takes 20 since 25 plus 20 = 45 half of 45 = 22.5 minutes. 22.2 minutes is erroneous due to 2 mowers cannot be in the same place at the same time

[@ryanseptember9058]

But they are not cutting half the lawn each. 1 cuts less than half and the other cuts more than half

[@gavindeane3670]

22.222222222 minutes (or to be more exact, 22 and two ninths minutes) is correct. You can easily see the problem with your method if you consider a more extreme example. Imagine Ed can mow the lawn in 100 seconds and Dave takes 100 days. Your method says that working together it would take them 25 days and 25 seconds. That's a bit more than a million seconds, whereas in fact it would take them slightly less than 100 seconds. Regardless of how fast they each are, it's obviously always going to be quicker for the two of them to work together than it would be for the faster guy to do the job on his own. But in my example, your method says that it takes Ed over 10,000 times LONGER to mow the lawn with Dave's help than it would take if Ed mowed it all on his own.

[@mahamunibalakrishnan8263]

D.22,2

[@russelllomando8460]

half the average... thanks for the fun.

[@nickcellino1503]

Half the average is 22.5 but the correct answer is 22.22...

[@gavindeane3670]

It's not half the average. The answer happens to be similar to half the average in this case because Ed and Dave work at quite similar rates. But in general, half the average has got nothing to do with how you answer a question of this form. Consider a more extreme example - say, Ed can mow the lawn in 100 seconds and Dave takes 100 days. The answer is nowhere near half the average.

[@russelllomando8460]

@@nickcellino1503 thanks...that was my baseline

[@richardevans6955]

Probably just me, but i got 9x over 200, 22x9 is 198, leaving 2/200, or 1/100, otherwise known as 1%. So why isn't the answer 22.1 minutes?

[@denisewenke8323]

When you get x by itself, you have 200/9, or 198/9 + 2/9.

[@tedfann3618]

Dave cute 1/2 the lawn in 25 min. and Ed cuts 1/2 the lawn 20 min. The only answer giving that is between 25 and 20 is 22.2 min. next question work smarter not harder

[@josephlaura7387]

d) 22.2min

[@panlomito]

Stupid multiple choice, so we are going to dart the answer... answer A and B are insane because slower than the fastest. So the answer will be C or D. Estimating (50 + 40)/ 2 = 45 minutes pp so the answer will be some around 22.5 minutes. So my best guess is answer D. But this puzzle is much nicer if we have a third party, so Adam and Ben in 50 minutes, Adam and Charles in 40 minutes, and Ben and Charles in 30 minutes... How fast will they do the job working all together?

[@garybernier7293]

If it were me and my dad, I couldn't do this right or that. It would take him hours just to explain it all. I do not work well with that man.

[@karendunning5594]

40 minutes. Hire Ed and tell Dave to #^^& off. 22.2 minutes is delusional.

[@jeffreyleonard7210]

Is 'mow the lawn' a euphamism?

[@user-pf9bv6dm5m]

If each cuts half the lawn it will take 45 min. 50/2 = 25 40/2 = 20. 25 + 20 = 45min

[@gavindeane3670]

They're working together rather than one after the other. They don't each cut half the lawn. Ed is faster than Dave so he will cut a bit more than half.

[@aljock6927]

The way I see it they had a fill up for gas check the oil and start it that equals 45 and then they're done Mowing and you're still figuring boring

[@afhtas]

You are assuming the have two lawn mowers. So the real life answer is 45 and 1/2 mins as I presume they are not taking over like a relay race. I did in fact get the right answer but then thought hang on. This is a trick question

[@UseR-ne8fm]

Content begins at min 3:00 ;)

[@johnrego3572]

22.2

[@samh-smith2931]

X/40(t) + Y/50(t) =50/50

[@samh-smith2931]

Insert 1min for time rather

[@sirtango1]

Man hours vs total time. Both are cutting at the same time.

[@paulm9954]

(50 * 40) / (50 + 40)

[@donaldmckinnie9461]

D 22.2 minutes

[@ekeleoseyeobhahinmejele2513]

22.2min

[@rusmanj.situmorang4166]

D. 22.2 minutes