4.7.1: Confidence intervals for population means. Jugp to level 1 Suppose the mean height in inches of all 9 th grade students at one high school is estimated. The population standard deviation is 4 inches. The heights of 9 randomly selected students are 75,72,69,65,73,74,65,69 and 71 x= Margin of error at 99% confidence level = 99%confidenceinterval=1 [smaller value, larger value].