Question

# If P(E) and P(E’) are the probabilities of two complementary events, then which of the following is always true?

A
P(E)+P(E)=0
B
P(E)+P(E)=1
C
P(E)=P(E)
D
P(E)+P(E)=12

Solution

## The correct option is B P(E)+P(E′)=1In a random experiment, the probabilities of all possible events must total to 1, which means some or the other outcome must occur on every trial. Now, in a complementary event there are only two possible outcomes. Thus, P(E) + P(E’) = 1. Or, the correct option is B.

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