Probability question I can't work out

[star01]

Hey

I've just joined here and I'm doing some revision on conditional probability. This one question, which I know should be simple, has me stumped. I've tried what I can think of but I can't seem to get it right. Any help anyone may have would be very much appreciated.

Suppose A and B are events and dene the new event C to occur if and only if
exactly one of A or B occur. Show algebraically, using only the probability axioms and
properties, and basic set-theoretic results given in the lectures, that
Pr(C) = Pr(A) + Pr(B) - 2Pr(A n B)

Thank you

 

[mathman]

C=(A-B) or (B-A), which are mutually exclusive events.. Evaluate probabilities to get result.