Definitions Complement rule: P(A^(C))=P(not A)=1-P(A) Addition rule for disjoint or mutually exclusive events: P(A ∪ B)=P(A or B)=P(A)+P(B) Solution A standard normal random variable is a continuous random variable. The probability that a continuous random variable is equal to 1 single value is always 0 (because the probability is the area and there is no area when we only have 1 single value). P(z=1)=0