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# Difficult probability question S1 watch

1. Hi,

P(A) = 0.4 and P(A u B) = 0.7

Find:

a) The P(A' n B)
b) The P(B) if A and B are mutually exclusive
c) The P(B) if A and B are independent.

I think a) is 0.3 and so is b)... but I'm not sure on c)

I know then P(A n B) = P(A) x P(B) but I can't work out P(B)!! I know that the probability of B without the intersect is 0.3...

Help me!!
Thanks!!
2. erm difficult?
3. haha well well
5. (Original post by CHEM1STRY)
Hi,

P(A) = 0.4 and P(A u B) = 0.7

Find:

a) The P(A' n B)
b) The P(B) if A and B are mutually exclusive
c) The P(B) if A and B are independent.

I think a) is 0.3 and so is b)... but I'm not sure on c)

I know then P(A n B) = P(A) x P(B) but I can't work out P(B)!! I know that the probability of B without the intersect is 0.3...

Help me!!
Thanks!!
P(A U B) = P(A) + P(B) - P(A n B)

But P(A n B) = P(A) x P(B)

Therefore P(A U B) = P(A) + P(B) - P(A) x P(B)

So P(B) = [P(A U B) - P(A)]/[1 - P(A)]

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