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The probability that neither occur is the complement of the
event that A or B occurs.
So we will first calculate P(A or B)
P(A or B) = P(A) + P(B) - P(A and B)
But since they are mutually exclusive, P(A and B) = 0
P(A or B) = P(A) + P(B) - P(A and B)
P(A or B) = P(A) + P(B) - 0
P(A or B) = P(A) + P(B)
P(A or B) = 0.21 + 0.05
P(A or B) = 0.26
The complement of the event (A or B) has probability
1 - 0.26 = 0.74
Edwin