Working together at their constant rates, A and B can fill

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Working together at their constant rates, A and B can fill [#permalink]

15 Jul 2010, 15:50

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Question Stats:

46% (01:53) correct

53% (00:37) wrong

based on 3 sessions

Working together at their constant rates, A and B can fill an empty tank to capacity in 1/2 hours. What is the constant rate of pump B?

(1) A's constant rate is 25 LTS / min
(2) The tanks capacity is 1200 lts.

[Reveal] Spoiler: OA

Last edited by Bunuel on 09 Nov 2012, 05:16, edited 1 time in total.

Edited the question.

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Re: Data sufficiency work rate problem [#permalink]

15 Jul 2010, 17:18

ksharma12 wrote:

15. working together at their constant rates , A and B can fill an empty tank to capacity in1/2 hr.what is the constant rate of pump B?
1) A's constant rate is 25LTS / min
2) the tanks capacity is 1200 lts.

Can someone solve this beyond just showing what is sufficient?

I know the answer is A but I need to know how to solve to fully grasp the concept of only needing the first statement.

Thank you

Question: If A and B can fill 2 tanks in 1 hour together, then how many tanks can B fill up in 1 hour alone?

I'm setting this up as ratios of "x tanks per 1 hour" :
\frac{a}{1hr}+\frac{b}{1hr}= \frac{2}{1hr}

1) This does NOT give you "a" because you need to know the size of the tanks. As we stated above, the ratios above show how many TANKS per hour each can fill, not how many gallons or liters. NOT sufficient

2) This gives you the tank's capacity, which is valuable in combination with 1). However, just knowing the tank's volume isn't useful since we don't know the flow rate of A. NOT sufficient

Now that we have both the flow rate and the volume of the tank, we can easily find the value of "a" in the above equation. Both statements together are sufficient.

Are you sure the answer is A? I definitely think it is C. Where is this question from?

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Re: Data sufficiency work rate problem [#permalink]

15 Jul 2010, 17:31

Yea i thought it was c too.

but its not.

This question is from the work/rate made easy thread in the beginning of the quant forum.

I figured knowing the rate per minute was not sufficient unless we knew the total.

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Re: Data sufficiency work rate problem [#permalink]

15 Jul 2010, 17:57

I'm definitely agreeing with you here. Must be a typo -- or we're both missing something obvious!

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Re: Data sufficiency work rate problem [#permalink]

16 Jul 2010, 02:08

(1/A+1/B)*0.5=1
It means that the work is done by 2 employees.
From (1) we have A, so we can solve for B.
That's all.
(A)

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Re: Data sufficiency work rate problem [#permalink]

16 Jul 2010, 08:10

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ksharma12 wrote:

Answer to this question is C not A.

rate*time=job.

We are told that (A+B)*30=C, where A is the rate of pump A in lts/min, B is the rate of pump B in lts/min and C is the capacity of the tank in liters.

Question: B=?

(1) A=25 --> (25+B)*30=C --> clearly insufficient (two unknowns), if C=1200, then B=15 but of C=1500, then B=25.

(2) C=1200. (A+B)*30=1200 --> A+B=40. Also insufficient.

(1)+(2) A=25 and A+B=40 --> B=15. Sufficient.

Answer: C.
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Re: working together at their constant rates , A and B can fill [#permalink]

25 Oct 2012, 07:25

Can't we do this question using unitary method ?

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Re: working together at their constant rates , A and B can fill [#permalink]

27 Dec 2012, 03:07

smartmanav wrote:

Can't we do this question using unitary method ?

Hi Smartmanav,

I guess this cannot be done by Unitary method as we are given the Constant rate of A i.e 25L/min. Now does it tell you the time A will take alone to fill the tank. No, because we do not the volume/size of the tank.

That is why method suggested by Bunuel of Rate*Time =Work

Thanks
Mridul

Re: working together at their constant rates , A and B can fill [#permalink] 27 Dec 2012, 03:07

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Working together at their constant rates, A and B can fill

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Working together at their constant rates, A and B can fill

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