Question

The number of ways in which we can select three numbers from the set {10,11, … ,100}, such that they form a GP with a common ratio greater than 1 is

(A) 18

(B) 19 

(C)  20 

(D)  None of these 

Answer 1

Correct option  (A) 18

Let the common ratio of GP be r and first term is a.

We have

So, there are 18 such terms.