Question

7. We want to estimate the mean amount of time people spend on Facebook each month.. How many randomly selected Facebook users must be surveyed if we want the sample mean to be in error by no more than 15 minutes, with a 95% confidence? A preliminary study suggests that the population standard deviation is 210 minutes.

Answer 1

Solution

standard deviation =   =210

Margin of error = E = 15

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* 210 / 15 )2

n =752.95

Sample size = n =753