A single letter is chosen at random from the world PROBABILITY. What is the probability of choosing a B or a P?

The total number of letters in the word PROBABILITY=11, of which two letters are B and one letter is P.

Let event A represent choosing the letter B.

P(A)=2/11

Let event B represent choosing the letter P.

P(B)=1/11

Because event A and event B have no outcomes in common, we can conclude that these two events are mutually exclusive and that

P(AB)=P(A)+P(B)=2/11+1/11=3/11