Question

A doctor at a local hospital is interested in estimating the birth weight of infants. How large a sample

must she select if she desires to be 98% confident that the true mean is within 2 ounces of the sample

mean? The standard deviation of the birth weights of a recent sample is known to be 8 ounces.

Answer 1

Solution :

Given that,

standard deviation =s =   =8

Margin of error = E = 2

At 98% confidence level the z is ,

= 1 - 98% = 1 - 0.98 = 0.02

/ 2 = 0.02/ 2 = 0.01

Z/2 = Z0.01 = 2.326 ( Using z table    )

sample size = n = [Z/2* / E] 2

n = ( 2.326* 8 / 2 )2

n =86.56

n= 87 rounded