Answer:
1
Step-by-step explanation:
If A and B are mutually exclusive and A is certain to happen, then B is certain to never happen, so P(B) = 0. The probability of either of two mutually exclusive events is the sum of their individual probabilities:
P(A or B) = P(A) +P(B) = 1 + 0
P(A or B) = 1
