The lengths of pregnancies are normally distributed with a mean of 273 days and a standard deviation of 20 days. If 64 women are randomly selected, find the probability that they have a mean pregnancy between 273 days and 275 days.

Answer 1

Use z-scores:

z = (275 - 273)/(20/√64) = ?

Once you calculate the z-score, check a z-table from mean to that z for your probability.

Answer 2

2/2.5 = 0.8 z=0.7881 1-0.7881 = 0.2119