In a toy box, suppose there are 22 marble balls (only blue or red) and 10 tennis balls (again, only blue or red). 4 of the tennis balls are blue, and 12 of the marble balls are red. If one ball is picked up randomly, determine the probability that the ball is either a tennis ball or red.
I am a beginner in probability but my guess is that it can be done by inclusion-exclusion.
P(T U R) = P(T) + P(R) - P(T&R) = (10/22) + (18/22) - (6/22)
Do I seem to be on the right track? Thanks for the help.
Yes, you can use inclusion-exclusion (or consider the complement as in the comment by @user2661923) but your calculation doesn't look quite right to me. All the denominators should be $32$, not $22$, since that's the total number of balls.