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.

What proportion of pregnancies will last between 240 and 270 days (8 and 9 months)? What proportion of pregnancies will last more than 300 days (8 and 9 months)?

What length of human pregnancies marks the shortest 70% of all pregnancies?