[求助]急！一道prep math 跪求解释

         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 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?

答案为 eleven

题目看不明白。。。跪求解释

        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 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?

8.1-(1.5*0.3) < X < 8.1+(1.5*0.3)

只有7.51不符合 所以有11個

原来如此多谢多谢~~~