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Confidence Interval

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A coal company wants to determine a 95% confidence interval estimate for the average daily tonnage of coal which they mine. Assuming that the company reports that the standard deviation of daily output is 80 tons, how many days should they sample so that the margin of error is 20 tons.

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Solution Summary

Provides steps necessary to determine the number of days the coal company should sample.

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The formula for a proportion confidence interval is:

mean ± z * standard deviation / square root of n

Here is what we know from the question:

For a 95% ...

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