Question

The length of a human pregnancy is normally distributed with a mean of 272 days with a standard deviation of 9 days (Bhat & Kushtagi, 2006). How many days would a pregnancy last for the shortest 20%? Round answer to 2 decimal places.

Answer 1

Answer:

Less than 264.44 days would be for the shortest 20%

Step-by-step explanation:

Given that X, the length of a human pregnancy is normally distributed with a mean of 272 days with a standard deviation of 9 days (Bhat & Kushtagi, 2006).

X is N(272, 9)

Corresponding Z score would be for any x

$z=\frac{x-272}{9}$

We have to find out the shortest 20%

Corresponding z score i.e. z score 20th percentile is given by

-0.84

corresponding x score is

$272-0.84*9\\= 264.44$

Less than 264.44 days would be for the shortest 20%