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If A and B are events with P(A) = 0.5, P(A OR B) = 0.65, P(A AND B) = 0.15, find P(B).

User JoseV
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1 Answer

4 votes

Answer:

P(B) = 0.30

Explanation:

This is a probability problem that can be modeled by a diagram of Venn.

We have the following probabilities:


P(A) = P_(A) + P(A \cap B) = 0.50

In which
P_(A) is the probability that only A happens.


P(B) = P_(B) + P(A \cap B) = P_(B) + 0.15

To find P(B), first we have to find
P_(B), that is the probability that only B happens.

Finding
P_(B):

The problem states that P(A OR B) = 0.65. This is the probability that at least one of this events happening. Mathematically, it means that:


1) P_(A) + P(A \cap B) + P_(B) = 0.65

The problem states that P(A) = 0.5 and
P(A \cap B) = 0.15. So we can find
P_(A).


P(A) = P_(A) + P(A \cap B)


0.5 = P_(A) + 0.15


P_(A) = 0.35

Replacing it in equation 1)


P_(A) + P(A \cap B) + P_(B) = 0.65


0.35 + 0.15 + P_(B) = 0.65


P_(B) = 0.65 - 0.35 - 0.15


P_(B) = 0.15

Since


P(B) = P_(B) + P(A \cap B)


P(B) = 0.15 + 0.15


P(B) = 0.30

User Jtahlborn
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