Assume that the distribution of the duration of human pregnancies can be approximated with a normal distribution with a mean of 266 days and a standard deviation of 16 days

a) What percentage of pregnancies should last between 260 and 280 days?

b) Find a value x such that 10% of the pregnancies of a duration that is longer than x days.

c) We select 500 pregnant women at random. Let N be the number of pregnancies in the sample with a duration between 260 and 280 days. Compute