prep关于标准差的一题 求助！谢谢

miweekend

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?


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) Four

(B) Six

(C) Nine

(D) Ten

(E) Eleven

voleroiseauer

mean=8.1 standard deviation=0.3
算出正负1.5方差的区间 [8.1-0.3*1.5,8.1+0.3*1.5]=>[7.65, 8.55]=11个？

miweekend

想请问为什么要0.3*1.5？谢谢！

whocatcher

我也做错过类似的题目的，看解析是这么算的，就记住了。真心不好意思，说

不出道道来，惭愧。。。话说答案是11个么？

miweekend

是11个 对的 没事儿 谢谢啦 我找不到这题的解析啊