30. Sample Size Using Range Rule of Thumb You want to estimate the mean amount of annual tuition being paid by current full-time college students in the United States the rule of thumb to make a rough estimate of the standard deviation of First use range the amounts spent. It is reasonable to assume that tuition amounts range from $0 to abour $45,000. Then use that estimated standard deviation to determine the sample size cor- responding to 99% confidence and a $100 margin of error. Does the resulting sample size seem practical?