A swimming pool is to be drained. The pool is shaped like a rectangular prism with length 30 feet, wide 18 ft, and depth 4ft. Suppose water is pumped out of the pool at a rate of 216ft3 per hour. If the pool starts completely full, how many hours does it take to empty the pool?

Answer: it will take 9 hours to empty the pool.

Step-by-step explanation:

The pool is shaped like a rectangular prism with length 30 feet, wide 18 ft, and depth 4ft. It means that when the pool is full, its volume is

30 * 18 * 4 = 2160 ft³

If water is pumped out of the pool at a rate of 216ft3 per hour, then the rate at which the water in the pool is decreasing is in arithmetic progression. The formula for determining the nth term of an arithmetic sequence is expressed as

Tn = a + d (n - 1)

Where

a represents the first term of the sequence (initial amount of water in the pool when completely full).

d represents the common difference (rate at which it is being pumped out)

n represents the number of terms (hours) in the sequence.

From the information given,

a = 2160 degrees

d = - 216 ft3

Tn = 0 (the final volume would be zero)

We want to determine the number of terms (hours) for which Tn would be zero. Therefore,

0 = 2160 - 216 (n - 1)

2160 = 216 (n - 1) = 216n + 216

216n = 2160 - 216

216n = 1944

n = 1944/216

n = 9