Question

Driving a piling into a harbor bottom, a pile driver sinks the piling 24 inches on the first stroke, 18 inches on the second stroke, and 13 1/2 inches on the third stroke. If the sequence is continued, how far will the piling be driven down on the 5th stroke?

Answer 1

7.6 inches to the nearest tenth.

Explanation:

18/24 = 3/4.

13.5 / 18 = 3/4.

This is a Geometric sequence with common ratio 3/4 or 0.75.

We need to find the fifth term of the sequence.

5th term = a1 (r)^(5 - 1)

= 24 * (0.75)^(5-1)

= 24 * 0.316406

= 7.6 inches.