Concept: The question tests the advanced understanding on Overlapping sets.

Solution:

Let Hockey = H ; Football= F ; Cricket = C

We know Total = H +C+ F - [(H∩C) + (C∩H) + (H∩F)] + (H∩C∩F) + Neither

=> 50 = 20+15+11 -[ 7+4+5 ] + (H∩C∩F) + 18

=> H∩C∩F = 2

Exactly two of these sports = Only HC + Only HC + Only HF

Number of students playing ONLY Hockey and Cricket

= (H∩C)-(H∩C∩F ) = 7 - 2 = 5

Number of students playing ONLY Cricket and Football

= (C∩F) - (H∩C∩F )= 4-2 = 2

Number of students playing ONLY Hockey and Football

= (H∩F) - (H∩C∩F ) = 5-2 = 3

Thus, number of students play exactly two of these sports. = 5+2+3=10 (Option B)