Question

5. An administrator wants to estimate the birth weights of babies in her hospital. How large a sample must be obtained if she desires to be 95% confident that the true mean is within a margin of error of 2 ounces? A similar sample taken the previous year yielded a standard deviation of 8 ounces. She will use this standard deviation. (10)

Answer 1

Solution

standard deviation =   =8

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

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

n = ( 1.96* 8/ 2 )2

n =61.4656

Sample size = n =61 rounded