Answer
See the answer below
Work Step by Step
General addition principale
$P(A\cup B)=P(A)+P(B)-P(A\cap B)$
Because the events are mutually exclusive, $P(A\cap B)=0$
Therefore $P(A\cup B)=P(A)+P(B)-0=P(A)+P(B)$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.