A population is estimated to have a standard deviation of 20

A population is estimated to have a standard deviation of 20. We want to estimate the population mean within 5, with a 95% level of confidence. How large of a sample is required?

Solution

Let sample size be n

Margin of error =5

i.e. 1.96 sigma/rtn = 5

rtn = 1.96*20/5 = 7.84

Square both sides

n = 61.46 or 62

Sample size = 62 is the answer