$A$ and $B$ are independent with $P(A) = 0.3$ and $P(B) = 0.6$. What is the probability that exactly one of them happens?

Explanation

1. 01

   $A$ only: $0.3 \times 0.4 = 0.12$; $B$ only: $0.7 \times 0.6 = 0.42$.

2. 02

   $0.12 + 0.42 = 0.54$.