## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$0.55$.
The Addition Rule of Probabilities says that: $P(A\cup B)=P(A)+P(B)-P(A\cap B)$. If A and B are mutually exclusive, then $P(A\cap B)=0$. Hence $P(A\cup B)=0.25+0.45-0.15=0.55$.