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# Confidence interval for a population mean

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A finance company needs to estimate the mean number of credit cards held by an American family. From past experience, the company knows that the standard deviation of the population is 1.16 cards. The company takes a random sample of n=31 families and finds the sample mean number of cards to be 4.6. Use this data to find a 90% confidence interval for u or mu.

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In this problem, we have a population with a known standard deviation. We are given the sample mean from sample of size 31 and asked to find the 90% confidence interval for the mean of the underlying population.

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Please see the attached MS Word document.

A 90% Confidence interval can be calculated as follows:

Where is the (1- )100th ...

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