SOLUTION: A doctor wants to estimate the HDL cholesterol of all​ 20- to​ 29-year-old females. How many subjects are needed to estimate the HDL cholesterol within 2 points with 99

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Question 1059759: A doctor wants to estimate the HDL cholesterol of all​ 20- to​ 29-year-old females. How many subjects are needed to estimate the HDL cholesterol within 2 points with 99% confidence assuming σ=10.2? Suppose the doctor would be content with 95 % confidence. How does the decrease in confidence affect the sample size​ required?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
The interval width is z*sigma/sqrt (n)=2; z(.995)=2.576.
Square everything
4=2.576^2*10.2^/n
N=690.386/4
=172.59 or 173
With 95%, z=1.96 and its square is 3.8416
The smaller value will lessen the numerator and decrease the sample size (to 100).
Less confidence with no other changes will cause a smaller sample size.