Confidence Intervals for Population Mean: Videos & Practice Problems

Researchers want to estimate the average cholesterol level of adult patients in a clinic. The lowest cholesterol level recorded is $120$ milligrams per deciliter and the highest is $240$ milligrams per deciliter. What is the minimum sample size needed to estimate the mean cholesterol level with $99\%$ confidence and a margin of error of $5$ milligrams per deciliter? Use the range rule of thumb to estimate the standard deviation.