Question

The pregnancy length in days for a population of new mothers can be approximated by a normal distribution with a mean of 265 days and a standard deviation of 12 days. What is the minimum pregnancy length that can be in the top 10​% of pregnancy​ lengths?

Answer 1

We have given following information,

Mean = days

Standard deviation = days

Calculating the z-value corresponding to top 10% i.e. 90th percentiles i.e. p = 0.90

z(p=0.10) = 1.28155 (From excel =NORM.S.INV (0.90))

Z = =

1.28155 =

X = (1.28155*12) + 265

X = 280.37

Minimum pregnancy length that can be in the top 10​% of pregnancy​ lengths is 280.37 days.