You are looking at the time it takes to finish these problem sets and you find the average time to complete these are normally distributed with a mean of 33 minutes and a standard deviation of 8 minutes

a) What is the probability one person takes longer than 40 minutes to do a problem set?

b) What is the probability a sample of 20 students will have an time to finish longer than 40 minutes?

c) Why is the answer for a) more than the answer for b)?