If a and b are dependent events, which of these conditions must be true?
a. p(a and b)=p(a) + p(b)
b. p(a and b)= p(b)
p(a)
c. p(b|a)=p(b)
d. p(a|b)=p(a)
e. p(b|a) does not equal p(b)

Two events are said to be dependent if the outcome or occurrence of the first affects the outcome or occurrence of the second so that the probability is changed. Also, Two events are said to be independent if the outcome or occurrence of the first does not affects the outcome or occurrence of the second so that the probability is not changed. For independent events: P(A and B) = P(A) x P(B). Recall that P(B|A) = P(A and B) / P(A) = P(A) x P(B) / P(A) = P(B). Therefore, for dependent events, P(B|A) is not equal to P(B).