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Given that A and B are independent and P(A)=1/5 and P(AUB)=1/4. Find
(a) P(A')
(b) P(B)
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(a) P(A') = 1 - P(A) = 1 - 1/5 = 4/5. (A' is the complement to B).
(b) Use the general formula, which is always valid
P(A U B) = P(A) + P(B) - P(A and B). (1)
Since A and B are independent, we have P(A and B) = P(A)*P(B) = .
Substituting the values into formula (1), we get
= + P(B) - .
Multiply both sides by 20
5 = 4 + 20*P(B) - 4*P(B)
5 - 4 = 16*P(B)
1 = 16*P(B)
P(B) = . ANSWER
Solved.