一道prep上面的题目，不知道大家有没有见过呢~

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 1000 cups dispensed by the vending machine,the 12 listed amounts, in ounces ,were selected from the data.If the 1000 recorded amounts have a mea of 8.1 ounces and a standard deviation of 0.3 ounces,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

Ans: 11

我看不懂，也不会做~~

还有一道题DS：

Malik's recipe for 4 servings of a certain dish requires 1又1/2cups of pasta.According to this recipe，what is the number of cups of pasta thta Malik will use the next time he prepares this dish？

1）The next time he prepares this dish，Malik will make half as many servings as he did the last time he prepare the dish

2）Malik used 6 cups of pasta the last time he prepared this dish.

答案是C

也是连题目都不懂~~唉~~

请大家一起想想吧~

standard deviation 就是标准差，代表数据偏离平均值（mean）的大小

问题是：这12个数里面有几个是在平均值的1.5倍标准差范围之内

8.1-0.3*1.5 <= x <= 8.1+0.3*1.5

DS 题的数学关系很简单，LZ主要可能被"the next time""the last time" confused

1)      告诉了下一次和上一次的关系，但没告诉上一次做了多少

2)      告诉了上一次做了多少，但不知道下一次要做多少

两个条件和起来就好了