If two events, A and B, cannot happen at the same time, they are called mutually exclusive.
The probability of A or B happening is the sum of their individual probabilities.
P (A or B) = P (A) + P (B)
A bag contains 4 red counters, 5 blue counters and 6 yellow counters.
One counter is selected at random.
What is the probability that it is red or yellow?
P(red) = 4/15
P(yellow) = 6/15
P(red or yellow) = 4/15 + 6/15 = 10/15 = 2/3