求教 标准差！

taohuaxian

7.51 8.22 7.86 8.36
8.09 7.83 8.30 8.01
7.73 8.25 7.96 8.53
A vending machine is designed to dispense 8 ounces of coffee into a cup. After a test that recorded the number of ounces of coffee in each of 1,000 cups dispensed by the vending machine, the 12 listed amounts , in ounces, were selected from the data. If the 1,000 recorded amounts have a mean of 8.1 ounces and a standard deviation of 0.3 ounce, how many of the 12 listed amounts are within 1.5 standard deviations of the mean?
答案有 4，6，9，10，11
正确答案是11
谢谢~

lindar1009

mean +- (s.d.*1.5), i.e. 8.1+0.3*1.5, 8.1-0.3*1.5, some value between 7.65 and 8.55... so there should be 11 listed amounts within those two figures..

bebeitts

额 8.1+0.3*1.5到8.1-0.3*1.5
就一个不在里面呀 看一下标准差定义..

taohuaxian

统计没学好啊  麻烦各位 !
谢谢~