19.12 Course grades. Choose a student at random from all who took the large accelerated introductory statistics at Hudson River College in the last 10 years. The probabilities for the student’s grade are
| Grade: | A | B | C | D or F |
| Probability: | 0.1 | 0.3 | 0.4 | ? |
(a) What must be the probability of getting a D or an F?
(b) To simulate the grades of randomly chosen students, how would you assign digits to represent the four possible outcomes listed?