Additive Rule in general:
P (A ∪B ) = P (A) + P (B ) – P (A ∩B )
If A and B are mutually exclusive:
P (A ∪B ) = P (A) + P (B )
Multiplicative Rule in general:
P (A ∩B ) = P (A)P (B| A)
If A and B are independent:
P (A ∩B ) = P (A)P (B)
A is 9 B is 2
I mean this has no calculous possible it is just to memorize the rules for the applications i guess