Question

Let R be a relation from the set {1, 2, 3………,60} to itself such that R = {(a, b) : b = pq, where p, q ≥ 3 are prime numbers}. Then, the number of elements in R is : 

(A) 600 

(B) 660 

(C) 540 

(D) 720

Answer 1

Correct option is (B) 660 

Number of possible values of a = 60, for b = pq, 

If p = 3, q = 3, 5, 7, 11, 13, 17, 19 

If p = 5 q = 5, 7, 11 

If p = 7 q = 7 

Total cases = 60 x 11 = 660