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Work/Ratio Problem

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

61% (01:53) correct 39% (01:01) wrong based on 31 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

[Reveal] Spoiler:
800score.com says it is D. I think it should be A

Let me know what you think- thanks-
Manager
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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)

Hope this helps
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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-
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Re: Work/Ratio Problem [#permalink]  17 Apr 2010, 11:48
why dont we read it CAREFULLY .....best thing is to read the question again before submitting the ans.
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Manager
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Re: Work/Ratio Problem [#permalink]  17 Apr 2010, 11:51
gurpreetsingh wrote:
why dont we read it CAREFULLY .....best thing is to read the question again before submitting the ans.

exactly
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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
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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
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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!

hope this has been clear and does make sense
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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.
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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

[Reveal] Spoiler:
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: 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.)
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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

[Reveal] Spoiler:
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

I agree- it's pretty clear. I just mis-read the question...
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Re: Work/Ratio Problem [#permalink]  08 May 2011, 22:36
Can someone please show how to solve this through algebra?
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Re: Work/Ratio Problem [#permalink]  08 May 2011, 23:16
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: Work/Ratio Problem [#permalink]  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
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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

So shortest time for 10 cars in 120 min...
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Re: Work/Ratio Problem [#permalink]  30 Oct 2011, 09:30
Quote:
I just overlooked this "independently" clause.

Like me !!
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Re: Work/Ratio Problem [#permalink]  30 Oct 2011, 11:15
omg I fell into trap...........interesting question
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Re: Work/Ratio Problem   [#permalink] 30 Oct 2011, 11:15
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