Question: The lengths of pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days.

a. One classical use of the normal distribution is a letter to "Dear Abby" in which a wife claimed to have given birth 308 days after a brief visit from her husband, who was serving in the Navy. Given this information, find the probability of a pregnancy lasting 306 days or longer. What does the result suggest?

b. A baby is said to be premature if the length of pregnancy is in the lowest 4%, find the length that separates premature babies from non premature babies.