5.20 Let the random variable X follow a normal distribution with m = 80 and s2 = 100.

a. Find the probability that X is greater than 60.

b. Find the probability that X is greater than 72 and less than 82.

c. Find the probability that X is less than 55.

d. The probability is 0.1 that X is greater than what number?

e. The probability is 0.6826 that X is in the symmetric interval about the mean between which two numbers?