The length of human pregnancies from conception to birth var

The length of human pregnancies from conception to birth varies according to a distribution that is approximately normal with mean 260 days and standard deviation 20 days. Use the 68-95-99.7 rule to answer the following questions.

A) How short are the shortest 2.5% of all pregnancies?

B) How long do the longest 2.5% of pregnancies last?

Solution

shortest 2.5% and longest 2.5% means 95% CI

A.) shortest 2.5% = mean - (2*s.d) = 260 - (2*20) = 220 days

B.) longest 2.5% = mean + (2*s.d) = 260 + (2*20) = 300 days