The volume of a rectangular swimming pool is 840 cubic meters and water is flowing into the swimming pool. If the surface level of the water is rising at the rate of 0.5 meters per minute, what is the rate, in cubic meters per minutes, at which the water is flowing into the swimming pool?
E. Not enough information to determine the rate
A qualitative approach to this one would be to imagine a 1 meter by 1 meter opening that's 840 meters deep. How much water is flowing in to raise the water level 0.5 meters per minute?
Then imagine a giant 40 meter by 21 meter pool that's only 1 meter deep. How much water does it take to raise the water level in that pool 0.5 meters? Put another way, how long will it take to fill if you raise the water level 0.5 meters per minute?
Since one pool fills in 2 minutes and the other takes... quite a bit longer... but they both have the same volume, you know you need more information.
Economist GMAT Tutor