Suppose the mean height in inches of all 9th grade students at one high school is estimated. The population standard deviation is 2 inches. The heights of 10 randomly selected students are 72, 70, 74, 71, 62, 65, 69, 65, 64 and 61. D = EX: 12.34 Margin of error at 90% confidence level = Ex: 1.23 90% confidence interval = [ Ex: 12.34 Ex: 12.34 [smaller value, larger value]