The standard IQ test is designed so that the mean is 100 and the standard deviation is 15 for the population of all adults. We wish to find the sample size necessary to estimate the mean IQ score of statistics students. Suppose we want to be 91% confident that our sample mean is within 2 points of the true mean. The mean for this population is clearly greater than 100. The standard deviation for this population is probably less than 15 because it is a group with less variation than a group randomly selected from the general population; therefore, we use sigma=15. we are being conservative by using a value that will make the sample size at least as large as necessaryAssume then that sigma = 15 and determine the required sample size .