Question

A researcher wishes to estimate the average number of minutes per day a person spends on the Internet. How large a sample must she select if she wishes to be 90% confident that the population mean is within 11 minutes of the sample mean? Assume the population standard deviation is 40 minutes. Round your final answer up to the next whole number.

Answer 1

solution :

Given that,

standard deviation =   =40

Margin of error = E = 11

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z _{0.05 = 1.645}

sample size = n = [Z/2 * / E] ²

n = ( 1.645 * 40 / 11)²

n =35.78214876

Sample size = n =36