Question

Do the following probabilities make sense? Explain.

P(A) = 1/5, P(B) = 1/3, and P(A or B) = 9/15
A. Yes; P(A or B) = P(A) + P(B)
B. Yes; P(A and B) = P(A) + P(B) - P(A or B)
C. No; neither P(A) nor P(B) can be greater than P(A or B).
D. No; P(A or B) cannot be greater than either of P(A) and P(B).

Answer 1

P(A) = 1/5, P(B) = 1/3

P(A or B) = P(A) + P(B) - P(A and B)

9/15 = 5/15 + 3/15 - x

9/15 = 8/15 - x

x = -1/15 (which does not make sense)

D. No; P(A or B) cannot be greater than either of P(A) or P(B).