# Probability Mutually exclusive events 5

Events A and B are mutually exclusive. Suppose event A occurs with probability $0.19$ and event B occurs with probability $0.72$. If A does not occur, what is the probability that B does not occur? Round your answer to at least two decimal places.

My answer is $0.09/0.81=0.11$

Yes.   But you really should show your work instead of just magic numbers. $$\begin{split}\mathsf P(B'\mid A')&=\dfrac{\mathsf P(B'\cap A')}{\mathsf P(A')}\\[2ex] &=\dfrac{1-\mathsf P(B)-\mathsf P(A)\require{cancel}\cancelto 0{+~\mathsf P(A\cap B)}}{1-\mathsf P(A)}\\[2ex] &= \dfrac{0.09}{0.81}\end{split}$$