Question

Assume that the mean length of a human pregnancy is 268 days with a standard deviation of 9 days. What percentage of human pregnancies do we expect to last no more than 260 days? ...?

Answer 1

The average time of pregnancy is 268 days (38 weeks and two days) from ovulation, with a standard deviation of 10 days or a coefficient of variation of 3.7%. Gestational age is calculated from the first day of the woman's last normal menstrual cycle.

However, only 5% of births occur on the expected date of delivery and at the age of 40 weeks of gestation. 50% of births occur one week before or one week after the expected date. 80% occurs between two weeks before or after

Answer 2

Assume that the mean length of a human pregnancy is 268 days with a standard deviation of 9 days. What precentage of human pregnancies do we expect to last no more than 260 days?

z(260) = (260-268)/9 = -8/9

P(x <= 260) = P(z <= -8/9) = normalcdf(-100,-8/9) = 0.1870