SOLUTION: In order to efficiently bid on a contract a contractor wants to be 95 % confident that his error is less than two hours in estimating the average time it takes to install tile floo

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Question 1080758: In order to efficiently bid on a contract a contractor wants to be 95 % confident that his error is less than two hours in estimating the average time it takes to install tile flooring. Previous contracts indicate that the standard deviation is 4.5 hours. How large a sample must be selected?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
In order to efficiently bid on a contract a contractor wants to be 95 % confident that his error is less than two hours in estimating the average time it takes to install tile flooring. Previous contracts indicate that the standard deviation is 4.5 hours. How large a sample must be selected?
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Since E = z*s/sqrt(n), n = [z*s/E]^2
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Your Problem:
n = [1.96*4.5/2]^2 = 20 when rounded up
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Cheers,
Stan H.
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