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Work/Ratio Problem [#permalink]
17 Apr 2010, 04:27

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This post was BOOKMARKED

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A

B

C

D

E

Difficulty:

5% (low)

Question Stats:

60% (01:53) correct
39% (01:01) wrong based on 23 sessions

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

Re: Work/Ratio Problem [#permalink]
17 Apr 2010, 04:53

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)

Re: Work/Ratio Problem [#permalink]
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-

Re: Work/Ratio Problem [#permalink]
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

Re: Work/Ratio Problem [#permalink]
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

Re: Work/Ratio Problem [#permalink]
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!

Re: Work/Ratio Problem [#permalink]
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.
_________________

He that is in me > he that is in the world. - source 1 John 4:4

Re: Work/Ratio Problem [#permalink]
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

Re: Work/Ratio Problem [#permalink]
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.)
_________________

He that is in me > he that is in the world. - source 1 John 4:4

Re: Work/Ratio Problem [#permalink]
20 Apr 2010, 04:23

hardnstrong wrote:

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

Re: Work/Ratio Problem [#permalink]
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