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Re: Data sufficiency work rate problem [#permalink]
15 Jul 2010, 16:18

1

This post received KUDOS

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?

Re: Data sufficiency work rate problem [#permalink]
16 Jul 2010, 07:10

1

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Expert's post

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

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.

Re: working together at their constant rates , A and B can fill [#permalink]
27 Dec 2012, 02:07

2

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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

_________________

“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”

Re: Working together at their constant rates, A and B can fill [#permalink]
29 Aug 2013, 17:13

1

This post received KUDOS

The standard formula for solving this problem is AB/A+B=1/2 hrs we need A to get to B, where A is the time taken by Pipe A to fill ENTIRE tank alone from options the time taken by Pipe A to fill ENTIRE tank alone=1200/25=48 minutes substitute in equation above to get value of B. SIMPLE!

gmatclubot

Re: Working together at their constant rates, A and B can fill
[#permalink]
29 Aug 2013, 17:13