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Before bidding, a contractor wants to be 90% confident that he is in error less than 20 min?

Before bidding, a contractor wants to be 90% confident that he is in error less than 20 minutes in estimating the average time it takes a certain kind of cement to dry. If the standard deviation, sigma, of the time it takes to dry can be assumed to be 60 minutes, on how large a sample should be base the estimate? Show all work a) n= b) What is the length of the 90% confidence interval?

Public Comments

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