find out the required sample size using the given data.
Choose an appropriate sample size
A personality test has a subsection designed to assess the "honesty" of the test-taker. Suppose that you're interested in the mean score, µ, on this subsection among the general population. You decide that you'll use the mean of a random sample of scores on this subsection to estimate µ. What is the least amount sample size needed in order for you to be 95 percent confident that your estimate is within 5 of µ? Use the value 20 for the population standard deviation of scores on this subsection.