Section 7.4 Probability Distribution (10 points) 11. a. A coin is flipped four times. Calculate and plot the distribution of the head and tail combinations. The combinations would be four heads; three heads and one tail; two heads and two tails; one head and three tails and four tails. (2 points) b. Corona virus infection recovery takes different period for different people. In a limited sample of 10 persons, the recovery period were 8, 9, 12, 4, 7, 21, 18, 13, 14, 11. Calculate the expected-value and variance of the sample. (2 points) c. The final exam of a discrete mathematics course consists of 50 true/false questions, each worth two points, and 25 multiple-choice questions, each worth four points. The probability that Linda answers a true/false question correctly is 0.9, and the probability that she answers a multiple-choice question correctly is 0.8. What is her expected score on the final? (2 points)