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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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.

(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)

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
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“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.”

So let's put this into an equation. We know that (Arate+Brate)30min=T, if T= the tank's capacity.

(1) now we know that Arate=25lirer/min, so we can plug that into the equation and we get (25lit/min+Brate)30min=T

This is not sufficient, because there are still too many unkowns. For example, it T=900 liters then Brate would equal 5 liters/min. But if T=9,000 then Brate would equal 275 liters/min

(2) now we know that T= 1200 liters, plugging that into the equation we get (Arate+Brate)30min=1200 liters

This is also not sufficient, because there are a variety of different combinations of Arate and Brate that can fit this equation. For example, Arate could be 10 liters per min and Brate could be 30 liters per min OR vice versa.

Now lets try them both together by plugging (1) and (2) into the equation:

(25lit/min+Brate)30min=1200 liters

divide both sides by 30 min and we get: 25 liters/min+Brate=40liters/min

that means Brate equals 15 liters, so the answer is (C) both together are sufficient

In the actual GMAT, you would not need to go so far as to figure out exactly what B rate. That would be a waste of time. As soon as you know what you CAN solve it with both, which can be determined by the fact that there is only 1 unknown then you should select C and move on.
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Eliza
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Imo C
At first sight the answer seems to be statement 1 but on closer inspection we come to know about its flaw as the rate is given in 25 liters per minute and from the question stem we have been given only the completion time ,So we need the capacity of the tank .
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