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Hi vaibhav101,

To start, you are not expected to know that a cubic cm = .001 liters. If this were an Official GMAT Question, then you would be given that 'conversion' in the prompt.

We're told that a water tank of 10,000 cm^3 capacity is to be filled from 2 taps: X and Y; the inflow of water from X is at the rate of 1 litre/min and the inflow from Y is 2.5 litres/min. We're asked for the number of MINUTES it will take for both the taps together to fill the whole tank. This question is essentially just a big 'rate' question, so you don't need to use the Work Formula to solve it.

Assuming that the tank starts off 'empty', the two taps will insert (1+2.5) = 3.5 liters/minute into the tank.

With a 10,000 cm^3 tank, you would need (10,000)(.001) = 10 liters of water to fill the tank

(10 liters)/(3.5 liters/min) = (10)/(7/2) = 20/7 minutes = 2 6/7 minutes

Final Answer: D

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vaibhav101 wrote:A water tank of $$10000\ cm^3$$ capacity is to be filled. There are 2 taps X and Y. Inflow of water through X is at the rate of 1 litre/min while through Y is 2.5litre/min. How many minutes will it take for both the taps together to fill the whole tank?

A 3.35
B 3.55
C 3.40
D 2.86
E 2.00

Since 1 liter = 1000 cm^3, we see that 10,000 cm^3 = 10 liters

The combined rate of the 2 taps is 3.5 litre/min.

So it will take 10/3.5 ≈ 2.86 minutes to fill the tank.

Answer: D