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Crew A can build a complete car in 20 minutes and Crew B can build a

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Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post Updated on: 15 Oct 2014, 10:54
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Difficulty:

  65% (hard)

Question Stats:

57% (01:47) correct 43% (02:03) wrong based on 362 sessions

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Crew A can build a complete car in 20 minutes and Crew B can build a complete car in 25 minutes. If both crews work independently and start at the same time, what is the shortest amount of time it could take for 10 cars to be complete?

A. 111 1/9 minutes
B. 115 2/5 minutes
C. 116 minutes
D. 120 minutes
E. 125 minutes

Originally posted by widerangeinput on 17 Apr 2010, 04:27.
Last edited by Bunuel on 15 Oct 2014, 10:54, edited 1 time in total.
Renamed the topic, edited the question and added the OA.
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 17 Apr 2010, 04:53
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IMO D

because in 100 min both crew will complete 9 cars (5 by crew A and 4 by crew B)
then crew a will finish the 10th car in next 20 min (before crew B which will complete their next care in 25 min, 5 min more than A)

Hope this helps
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 17 Apr 2010, 05:41
hardnstrong wrote:
IMO D

because in 100 min both crew will complete 9 cars (5 by crew A and 4 by crew B)
then crew a will finish the 10th car in next 20 min (before crew B which will complete their next care in 25 min, 5 min more than A)

Hope this helps


I just overlooked this "independently" clause. Just did the 1/20+1/25 thing... Thank you-
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 17 Apr 2010, 11:48
why dont we read it CAREFULLY :P .....best thing is to read the question again before submitting the ans.
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 19 Apr 2010, 10:23
please forgive me....but would you mind spelling out why working independently has an effect? Unfortunately I still don't get it.....even if they work independently, aren't at total of 10 cars completed between the two of them? Thanks
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New post 19 Apr 2010, 10:24
please forgive me....but would you mind spelling out why working independently has an effect? Unfortunately I still don't get it.....even if they work independently, aren't at total of 10 cars completed between the two of them? Thanks
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New post 19 Apr 2010, 10:38
PeterFaulkner wrote:
please forgive me....but would you mind spelling out why working independently has an effect? Unfortunately I still don't get it.....even if they work independently, aren't at total of 10 cars completed between the two of them? Thanks


welll, A can build a car in 20 minutes and B in 25. So if they both utilize their production capabilities and work on a single car together, this should logically take less than 20 minutes for sure. (Think of it like, A is working on a car and B is helping A at the same time- this should definitely take way less then 20 minutes...)
mathematically:
it's 1/20+1/25=9/100 where it takes 100/9 hours to build a single car. Thus it takes 111 1/9 hours to complete 10 of them. And here you go- the guys put this one into the very first choice so that you'll fall into that trap!

hope this has been clear and does make sense
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 19 Apr 2010, 11:26
I strongly dislike this question. If we’re to assume that rates can be fractional then why can’t the same be assumed for work also? I wonder if the GMAC would put something this ambiguous on the real test.
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 20 Apr 2010, 00:46
widerangeinput wrote:
Crew A can build a complete car in 20 minutes and Crew B can build a complete car in 25 minutes. If both crews work independently and start at the same time, what is the shortest amount of time it could take for 10 cars to be complete?

A. 111 1/9 minutes
B. 115 2/5 minutes
C. 116 minutes
D. 120 minutes
E. 125 minutes

800score.com says it is D. I think it should be A


Let me know what you think- thanks-



read the question carefully. the red highlighted part. How can you combine when question clearly says they both work independently
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 20 Apr 2010, 03:55
if the question said 10 whole cars then i'd say "okay that makes sense" but even from an accounting perspective inventory is recorded by the percentage of its completion and added up (not that that applies here. i'm just saying that there is nothing that explicitly states that it doesn't apply.)
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 08 May 2011, 23:16
1
Good question indeed.

Let crew A works for x min and crew B works for y min independently for 10 cars

crew A makes 1/20 car/ min and crew B makes 1/25 car / min

then, x*(1/20) + y*(1/25) = 10 Taking LCM for 20 and 25 min = 100.

Means when x=y = 100 mints each, number of cars = 5+4 = 9.
Crew A finishes a car faster than crew B.

hence 100 + 20 = 120 will be the time needed for 10 cars.
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 10 May 2011, 06:58
A builds 4 cars in 80 min

B builds 4 cars in 100 min

So A builds another car in another 20 min (i.e total 5 cars)

B builds another car in another 25 minutes (i.e, total 5 cars)

However, A can build another car in next 20 min (i.e total 6 cars)

So total time = 125 min by B, which is > 120 min by A

B - 4 cars, A - 6 cars
Answer = D
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 10 May 2011, 09:27
Take the one that needs less time i.e. 20 min...
20 min*5 = 100 min
So total 9 cars can be made in 100 min (5 from A and 4 from B)
So one more car would need 20 more min

So shortest time for 10 cars in 120 min...
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 30 Oct 2011, 11:15
omg I fell into trap...........interesting question
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 15 Oct 2014, 12:13
widerangeinput wrote:
Crew A can build a complete car in 20 minutes and Crew B can build a complete car in 25 minutes. If both crews work independently and start at the same time, what is the shortest amount of time it could take for 10 cars to be complete?

A. 111 1/9 minutes
B. 115 2/5 minutes
C. 116 minutes
D. 120 minutes
E. 125 minutes


Ha Ha Ha Ha..

Awesome question. Its easy and has a trap. I fell into it. As soon as I read Time taken to complete cars, started solving by Work ratio method...

Later on realized my mistake...
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 30 Nov 2017, 08:00
I'm not fully clear neither algebra solution nor the shortcut way.
Can anyone please elaborate clearly on this question?
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a  [#permalink]

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New post 30 Apr 2018, 05:36
A tricky one indeed !!! Note that the question wants us to find the least number of minutes when the two are working independently. In 100 min Crew A makes 5 and Crew B makes 4 cars. Tenth car will take 20 min for Crew A. Minimum of 120 minutes will be required. Option D it is !!
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Re: Crew A can build a complete car in 20 minutes and Crew B can build a &nbs [#permalink] 30 Apr 2018, 05:36
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