Question 1143166: The pregnancy length in days for a population of new mothers can be approximated by a normal distribution with a mean of 271 days and a standard deviation of 7 days.
A. What is the minimum pregnancy length that can be in the top 13% of pregnancy lengths?
B. What is the maximum pregnancy length that can be in the bottom 9% of pregnancy lengths?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! For the top 13% of lengths the z value is +1.127
z=(x-mean)/sd
1.127=(x-271)/7
x=271+7.889 or 278.9 days for minimum length
For the bottom 9% it will have a z=-1.34
The calculations will show 261.6 days
on calculator, 2nd VARS 3 for inv-norm
type in decimal (so top 13% is 0.87 and bottom 9% is 0.09), then comma, then mean, then comma, then sd, then ENTER.
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