A swimming pool has a volume of 2400 ft3 and is filled to 8 feet. The owners are draining the pool at 30 ft3 per minute. After how long is the pool 6 feet deep?

We determine first the area of the base of the pool given that its height is approximately 8 ft by dividing 2400 ft³ by 8 ft. This gives us an answer of 300 ft².

Then, we determine the volume of the pool when it is only 6 ft deep. That is 300 ft² x 6 ft = 1800 ft³. Subtracting this value from the original volume will give us an answer of 600 ft³. Given that the pool is drain at a rate of 30ft³/min, the amount of time needed to drain the pool to 6 ft is equal to 20 minutes.