- #1

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## Homework Statement

If P(A) = .4, P(B) = .5 and P(A and B) = .1, find P(A or B)

## Homework Equations

## The Attempt at a Solution

Why isn't the answer just .9, add the two probabilities together? The book says the answer is .8

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- Thread starter g.lemaitre
- Start date

- #1

- 267

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If P(A) = .4, P(B) = .5 and P(A and B) = .1, find P(A or B)

Why isn't the answer just .9, add the two probabilities together? The book says the answer is .8

- #2

- 267

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I got it now. I didn't see this equation

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

.4 + .5 - .1 = .8

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

.4 + .5 - .1 = .8

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