Question

The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days. At what percentile is a pregnancy that lasts 240 days (that's about 8 months)?

Answer 1

5.21-th

Explanation:

Mean pregnancy time (μ) = 266 days

Standard deviation (σ) = 16 days

The z-score, for any given pregnancy period 'X' is determined by:

`z=(X-\mu)/(\sigma)`

For X = 240 days:

`z=(240-266)/(16)\\ z=-1.625`

According to a z-score table, a score of -1.625 is equivalent to the 5.21-th percentile of a normal distribution