SOLUTION: Given that P(A or B) = ½, P(A) = 1/3, and P(A and B) = 1/9, find P(B).

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Question 1147922: Given that P(A or B) = ½, P(A) = 1/3, and P(A and B) = 1/9, find P(B).

Answer by ikleyn(52841) About Me  (Show Source):
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Use the general formula


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


Substitute the given data into the formula to get an equation


    1%2F2 = 1%2F3 + P(B) - 1%2F9.


From the equation, find


    P(B) = 1%2F2 - 1%2F3 + 1%2F9 = 9%2F18+-+6%2F18+%2B+2%2F18 = 5%2F18.    ANSWER.

Solved.