Working at a constant rate respectively pumps X and Y took

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GMAT Prep

Working at a constant rate respectively, pumps X and Y took 48 hours to fill an empty water tank. What fraction of the water in a full tank came from pump X?

1) working alone at its constant rate, pump X would have taken 80 minutes to fill tank with water.
2) working alone at its constant rate, pump y would have taken 120 minutes to fill up the tank.

OA D

[Gene@KaplanGMAT]

The combined work formula for the 2 pumps would be (XY)/(X+Y) = 48 hours, where X is the number of hours it would take X by itself to fill the water tank, and Y is the number of hours it would take Y by itself to fill the water tank.

We have 2 variables but only 1 equation. So if we can get one more distinct equation, we'll have sufficiency.

Statement (1) ----> X = 80 minutes = 1.33 hours. This would enable us to solve for Y in the equation above, and subsequently what fraction of the full tank came from Pump X. SUFFICIENT

Statement (2) ----> Y = 120 minutes = 2 hours. This would enable us to solve for X in the equation above, and subsequently what fraction of the full tank came from Pump X. SUFFICIENT.

Each statement is sufficient. Answer is (D).