A study of cars on a highway showed that 70% had only one occupant, 15% had 2, 10% had 3, 3% had 4, and 2% had 5. Let X represent the number of occupants in a randomly chosen car.

a. Write the probability mass function of X.
b. Write the cumulative distribution function of X.
c. Find the probability that X is less than or equal to 2.
d. Find the probability that X is greater than 3.
e. Find the expected value of X.
f. Find the variance of X.