Solution. a) Since the probability of showing the letter A is and the probability of showing the letter B is the probability of showing the letter A or B is the

a) Since the probability of showing the letter A is and the probability of showing the letter B is the probability of showing the letter A or B is the probability of showing the letter A or B is

b) The probability of not showing the letter C can be done in two ways. We can use the complement and state that

Alternatively, we can see that this is the same as showing a letter A or B and hence is the same as the answer to part a.