Question

Pregnancy length (in days) has a normal probability distribution with a mean of 266 days and a standard deviation of 16 days. What is the length of the pregnancy that marks the start of the 25th percentile? Enter a number rounded to two decimal places. Do not enter the units.

Answer 1

264.20

Explanation:

Let X be the pregnancy length (in days)

Then X is N(266,16)

We can convert X to Z by

`(x-266)/(16)`

`Z=(x-266)/(16)` is N(0,1)

25th percentile for Z is

-0.675

Convert back to x score

`x=-0.675(16)+275\\X =264.20`

25th percentile is 264.20