A probability sets question...please help:)

Carisma · 2010-01-08 01:19:00

Given that events A and B are independent with P(A n B)=0.3 and P(A u B')=0.3, find P(A u B).

It's supposed be quite basic as its only 3 marks, but I think I'm missing something as I can't figure it out...anyone know?

Thank you for your help

Last edited by Carisma (2010-01-08 01:19:29)

mathsyperson · 2010-01-08 01:39:27

I think there may be a mistake with the question, because I didn't use their independence and it just doesn't seem right.

Taking P(A u B') = 0.3 and negating it, we get P(A' n B) = 0.7.
Since we also have that P(A n B) = 0.3, we now know that P(B) = 1.

Hence, P(A u B) = 1 also.

bobbym · 2010-01-08 01:44:58

Hi Carisma;

A and B are independent with P(A n B)=0.3

I agree if they were independent how could the intersection of A , B be anything but 0?

Welcome to the forum!

mathsyperson · 2010-01-10 07:17:54

You're thinking of mutually exclusive. If events A and B are independent it means that P(B) = P(B|A) = P(B|A'), and vice versa.

bobbym · 2010-01-10 15:31:27

Hi,

Yep, definitions, I can never remember them.

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