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 1.2 kWh. The mean electricity usage per family was found to be 17 kWh per day for a sample of 397 families. Construct the 80% confidence interval for the mean usage of electricity.

Round your answers to one decimal place.

Answer #1

80% confidence interval for is

- Z/2 * / sqrt(n) < < + Z/2 * / sqrt(n)

17 - 1.2816 * 1.2 / sqrt(397) < < 17 + 1.2816 * 1.2 / sqrt(397)

16.9 < < 17.1

80% CI is **( 16.9 , 17.1 )**

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