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# Confidence interval for a population proportion

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The lifetime of a certain brand of battery is known to have a standard deviation of 11.3 hours. Suppose that a random sample of 90 such batteries has a mean lifetime of 33.4 hours. Based on this sample, find a 95% confidence interval for the true mean lifetime batteries of this brand. What is the lower limit of the 95% confidence level? What is the upper limit?

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How to find upper and lower limit of a confidence level
The lifetime of a certain brand of battery is known to have a standard deviation of 11.3 hours. Suppose that a random sample of 90 such batteries has a mean lifetime of 33.4 hours. Based on this sample, find a 95% confidence interval for the true mean lifetime ...

#### Solution Summary

This solution shows step-by-step how to construct and interpret a confidence interval for a population proportion.

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