statistics
posted by Tian .
From past experience it is felt that the random variable, X, the age of a mother at the birth of her first child, is normally distributed with a mean of 21.3 and a variance of 16. Find the probability that a randomly selected mother:
(a) has her first child before age 16
(b) has her first child after age 30
(c) has her first child between the ages of 15 and 20
(d) has her first child between the ages of 14 and 28

Z = (scoremean)/SD
variance = SD^2
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores.