13.15 Length of pregnancies. The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days. Use the 68–95–99.7 rule to answer the following questions.
(a) Almost all (99.7%) pregnancies fall in what range of lengths?
(b) How long are the longest 2.5% of all pregnancies?