CHALLENGE ACTIVITY 6.2.1: Confidence intervals for population means. 377136.2340164.qx3zqy7 Jump to level 1 1 Suppose the mean height in inches of all 9th grade students at one high school is 2 estimated. The population standard deviation is 2 inches. The heights of 8 randomly selected students are 75, 74, 60, 74, 70, 61, 70 and 64. ac = 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]