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 95% confident that her estimate is within 2 ounces of the true mean? Assume that s = 6 ounces based on earlier studies.

Answer 1

Solution

standard deviation = =6

Margin of error = E = 2

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z/2 = Z0.025 = 1.96 ( Using z table ( see the 0.025 value in standard normal (z) table corresponding z value is 1.96 )

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

n = ( 1.96* 6/2 )2

n =34.5744

Sample size = n =35