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.
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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