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Problem 18 - Entrance Test

A water tank can hold 1000 liters of water. Due to a leak, the tank is losing water at a rate of 5 liters per minute. At the same time, water is being added to the tank at a rate of 10 liters per minute. How many minutes will it take to fill the tank?

Correct: D

The net rate at which the tank is being filled is the difference between the rate at which water is being added and the rate at which it is leaking out: 10 liters/minute - 5 liters/minute = 5 liters/minute. To find the time to fill the tank, divide the capacity of the tank by the net fill rate: 1000 liters / 5 liters/minute = 200 minutes.