Question

3. If A and B are complements, P(A)= a, and P(B)=b, which of the following must be true?

(1) a=b+1
(3) a=1-b
(2)a= 1/b
(4) a=b-1

Answer 1

(3) a = 1 - b

Explanation:

since A and B are complements, it means that together they are the whole.

the probability of the whole is 1.

so,

a + b = 1

therefore,

a = 1 - b