A company president wishes to estimate the average number of hours his part-time employee per week. The standard deviation from a previous study is 9.3 hours. How large a sample must be selected if he wants to be 99% confidence of finding whether the true mean differs from the sample mean by 4 hours

Let us imagine that you own a fast-food company. You are doing a survey to get an idea of how long customers stay in a restaurant. In the past two years, it was observed that the standard deviation of the time they stay in a restaurant is restaurant is 12 minutes. How many people do you need to observe so that the desired margin of error will not be more than three (3) minutes with a confidence level of 95%? 

A school principal wants to estimate the average score of their students on a standardized test. The standard deviation from a previous study is 12 points. How large a sample must be selected if they want to be 95% confident of finding whether the true mean differs from the sample mean by 6 points?

A researcher wants to estimate the average weight of newborn babies in a certain region. The standard deviation from a previous study is 0.5 kilograms. How large a sample must be selected if they want to be 90% confident of finding whether the true mean differs from the sample mean by 0.2 kilograms?

A city council is interested in estimating the average monthly water consumption per household. The standard deviation from a previous study is 20 gallons. How large a sample must be selected if they want to be 99% confident of finding whether the true mean differs from the sample mean by 5 gallons?