If the fifth term of a GP is 81 and first term is 16, what will be the 4th term?

A 9

B 18

C 36

D 54

Correct Answer: Option D

5th term of GP = ar⁵−1 = 16×r⁴ = 81
Or, r = (81/16)^¼ = 3/2

4th term of GP = ar⁴−1 = 16×(3/2)³ = 54