SOLUTION: P(A or B) =1/4, P(A)=1/7, and P(AandB)=1/9, FindP(B)

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Question 980568: P(A or B) =1/4, P(A)=1/7, and P(AandB)=1/9, FindP(B)
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Let x = P(B)


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


1/9 = 1/7 + x - 1/9


1/9 + 1/9 = 1/7 + x - 1/9 + 1/9 ... Add 1/9 to both sides


2/9 = 1/7 + x


x + 1/7 = 2/9


x + 1/7 - 1/7 = 2/9 - 1/7 ... Subtract 1/7 from both sides.


x = 2/9 - 1/7


x = 14/63 - 9/63


x = 5/63


So, P(B) = 5/63