Question

The electric cooperative needs to know the mean household usage of electricity by its non-commercial customers in kWh per day. They would like the estimate to have a maximum error of 0.12 kWh. A previous study found that for an average family the variance is 2.56 kWh and the mean is 15.5 kWh per day. If they are using a 98% level of confidence, how large of a sample is required to estimate the mean usage of electricity? Round your answer up to the next integer.

Answer 1

Solution :

Given that,

Population standard deviation () = = 2.56

= 1.6

Margin of error = E = 0.12

Z/2 = 2.326

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

n = [2.326 * 1.6/ 0.12]2

n = 961.82

The sample size is required = 962