You want to estimate the average income for uninsured adults in Utah. You will do this by conducting a survey of uninsured adults. You know the standard deviation of incomes in this population is $15,000. You want a margin of error on your estimate of no more than $2,500 at a 95% confidence level. At least how many adults do you need to survey?

Find the critical value for the following tests:

One-sided Z-test at a 95% confidence level

Two-sided Z-test at a 95% confidence level

One-sided t-test at a 95% confidence level with 25 degrees of freedom

Two-sided t-test at a 95% confidence level with 12 degrees of freedom