The lengths of pregnancies of humans are normally distributed with a mean of 268 days and a standard deviation of 15 days. A baby is premature if it is born three weeks early. What percent of babies are born
Prematurely?
A)8.08%
B)6.81%
C)9.21%
D)10.31%

Question

Quizplus · Accepted Answer

Three weeks early is 21 days early. The z-score for this is (21 - 268) / 15 = -1.62. The area to the left of this z-score is 0.0526, or 5.26%. So, the percent of babies born prematurely is 100% - 5.26% = 94.74%.

The Lengths of Pregnancies of Humans Are Normally Distributed with a Mean