# Confidence Interval for Mean

Average electric usage was studied. A previously known population standard deviation was 450 KWH. A sample of 81 houses was studied and found to have a mean of 1858 KWH.

Find the 95% confidence interval for the true mean.

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#### Solution Preview

The formula for a proportion confidence interval is:

mean ± z * standard deviation / square ...

#### Solution Summary

The 95% confidence interval for the true mean is determined.

$2.19