Question

In proportion, the 1st, 2nd, and 4th terms are 51, 68, and 108 respectively. Find the 3rd term.

Answer 1

Let the 3rd term be x.
Thus, 51 : 68 :: x : 108
 We know:
Product of extremes = Product of means
51 × 108 = 68 × x
⇒ 5508 = 68x
⇒  x = `5508/68` = 81

Hence, the third term is 81.