Dear student,
An intersection of two events means that the common part of two events. That is if A and B are two events then
AB denotes the common part of it. ABA, and ABB.
Now P(AB)=P(A)+P(B)-P (AB) so P (AB) = P(A)+P(B)- P(AB)
But if two events are independent of each other then you can find P (AB) just by multiplying the probabilities of those two events. i.e. P (AB)=P(A).P(B)
regrades