Question
Surjit and Sachdev appeared for an interview. The probability of their selection is 
respectively. Find the probability only one of them selected.
Solution
Let A : Surjit is selected
B ; Sachdev is selected
P(only one is selected) = P('A and not B' or 'B and not A')
= P(A and not B) + P(B and not A)
= P(A) P(not B) + P(B) P(not A)
= P(A) [1 - P(B)] + P(B) [1 - P(A)]
