求教一题prep math

eaky

121. 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?
(A) Four
(B) Six
(C) Nine
(D) Ten
(E) Eleven
E
怎么算的啊@@。。。

andrewsun

121. 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?
(A) Four
(B) Six
(C) Nine
(D) Ten
(E) Eleven
E
怎么算的啊@@。。。

-- by 会员 eaky (2009/11/14 22:56:12)

条件没写全。。。人家原来还有这12个数字的样本呢
7.51 8.22 7.86 8.36
8.09 7.83 8.30 8.01
7.73 8.25 7.96 8.53
只有7.51不在8.1+/-0.45之间

eaky

恩。。。我后来发现漏题目条件了。。。

0.45的算法是不是0.3*1.5？最后一句话的意思就是要求在标准差的1.5倍范围内咯。谢谢~