P(a or b)=0.7, p(b)=0.5, p(a|b)=0.2 find p(a)

Answer 1

P(A|B) = P(A and B)/P(B)

P(A and B) = P(B) P(A|B) = 0.5 * 0.2 = 0.1

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

0.7 = P(A) + 0.5 - 0.1

0.3 = P(A)