Question

You want to study the average time per day spent on using mobile phones by students at an university. Your goal is to provide a 95% confidence interval estimate of the mean time per day. Previous studies suggest that the population standard deviation is about 4 hours per day. What sample size (at a minimum) should be used to ensure the the sample mean is within

(a) 1 hour of true population mean?

(b) 0.5 hour of true population mean?

Answer 1

Given that, population standard deviation = 4 hours

A 95% confidence level has significance level of 0.05 and critical value is,

We want to find, the sample size ( n ), for following margin of errors,

a) For margin of error ( E ) = 1 hour

Therefore, required sample size is 62

b) For margin of error ( E ) = 0.5 hour

Therefore, required sample size is 246