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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? DON'T JUST GIVE THE ANSWER - SHOW WORK AND EXPLAIN YOUR PROCESS EACH STEP OF THE WAY SO THAT I CAN FOLLOW WHAT YOU DID AND CHECK YOUR WORK.

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Answer:

Step-by-step explanation:

Given that 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.

Std deviation =4.5 errors

95% confidence interval = Mean±1.96*std dev

Hence we have

[tex]1.96(\frac{4.5}{\sqrt{n} } )<2[/tex]

[tex]\sqrt{n} \geq 4.41\\n\geq 19.4481[/tex]

Sample size should be 20.

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