问一道数学题哈

蓝兰紫籽 · 发表于 2012-4-1 20:58:57

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

求详细的解释啊，LZ数学烂~~~祝各位好心人都上7

蓝兰紫籽 · 发表于 2012-4-2 12:57:10

你题目少条件了 http://www.urch.com/forums/gmat-problem-solving/48147-vending-machine.html

-- by 会员 nicolaszou (2012/4/1 21:15:20)

谢谢，怪不得我觉得这题怎么这么难

Plusone · 发表于 2012-4-1 23:45:33

正态分布知识
μ-σ,μ+σ区间：68.27%
μ-2σ,μ+2σ区间：95%
μ-3σ,μ+3σ区间：99%
1.5倍标准差，大致是1和2之间，算出来除以2

nicolaszou · 发表于 2012-4-1 21:15:20

你题目少条件了 http://www.urch.com/forums/gmat-problem-solving/48147-vending-machine.html

问一道数学题哈

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