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

Sample size should be 20.
Answer:
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Step-by-step explanation:
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<span><u>Possible correct answers</u> are:
20%+15%; and 50% of 70%.
Explanation<span>:
Benchmark percents are percents that are commonly used. 20% and 15% are two commonly used percentages; the sum of them would be
20%+15% = 35%.
A multiple of a percent is a percent of a percent. Taking 50% of 70% of a number is the same as multiplying by 0.5(0.7) = 0.35.</span></span>