THE GATEBOOK

Normalization Lectures

Three squares of chess board are selected at random. The probability of getting 2 squares of one colour and other of a different colour is

A. 16/21

B. 8/21

C. 3/32

D. 3/8

ANS A.

Total boxes in chess of 8*8= 64.

choosing any 3 squares= 64C3.

Choosing such that we have 2 of one colour and 1 of other colour.

So, 2B and 1W or 1W or 2B. (2 possibilities).

Required probability= (32C2 * 32C1) * 2 / 64C3= 16/21