Question

The electric cooperative needs to know the mean household usage of electricity by its non-commercial customers in kWh per day. Assume that the population standard deviation is 2.3 kWh. The mean electricity usage per family was found to be 15.3 kWh per day for a sample of 3611 families. Construct the 99% confidence interval for the mean usage of electricity.

Answer 1

Solution :

Given that,

Sample size = n = 3611

Z_/2 = 2.576

Margin of error = E = Z_/2* ( /n)

= 2.576 * (2.3 / 3611)

Margin of error = E = 0.1

At 99% confidence interval estimate of the population mean is,

- E < < + E

15.3 - 0.1 < < 15.3 + 0.1

15.2 < < 15.4

(15.2 , 15.4)