Question

Let a and b be any two events defined on the sample space s. suppose that p(a) = 0.4, p(b) = 0.5, and p(a∩b) = 0.1. what is the probability that a or b but not both occur?
a. 0.9
b. 0.8

Answer 1

Are these really the only options? Because it seems to me that

$P((A\cup B)\cap(A\cap B)^C)=P(A\cup B)-P(A\cap B)$

$=P(A)+P(B)-2P(A\cap B)$

$=0.7$