Question

In order to estimate the average electric usage per month, a sample of 196 houses was selected and their electric usage was determined. Assume a population standard deviation of 350 kilowatt-hours. If the sample mean is 2000 kWh, what is the 94% confidence interval estimate of the population mean?

Answer 1

given data are:-

sample size (n) = 196

sample mean () = 2000

population sd () = 350

z critical value for 94% confidence level ,both tailed test be:-

[ alpha= (1-0.94) = 0.06

as this is a both tailed test alpha/2 = 0.06/2 =0.03

in any blank cell of excel type =NORMSINV(0.03) press enter.

you will get -1.88079.take the absolute value as critical value ]

the 94% confidence interval estimate of the population mean be:-

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