求教一道PREP模考里的数学题

乔小桥

The residents of Town X participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours. The number of hours that pat, a resident of Town X, watched television last week was between 1 and 2 standard deviations below the mean. Which of the following could be the number of hours that Pat watched television last week.

○30

○20

⊙18

○12

○6

实在抱歉，答案是12, 我看错了，不好意思不好意思，我明白这题了，谢谢回答问题的两位童鞋

jessie10

between 1 and 2 standard deviations below the mean就是1*6--2*6之间，在21减去这个范围，所以就是15和19范围之间，选18。

cindytim

你在好好减减， 方法对了。
在9--15之间取值

乔小桥

between 1 and 2 standard deviations below the mean就是1*6--2*6之间，在21减去这个范围，所以就是15和19范围之间，选18。

-- by 会员 jessie10 (2010/4/8 11:22:14)

谢谢，我懂了~

乔小桥

你在好好减减， 方法对了。
在9--15之间取值

-- by 会员 cindytim (2010/4/8 11:26:44)

谢谢，原来这么简单。我脑残了。。

flyingbunny

答案看错了吧？

应该是12.

http://www.manhattangmat.com/forums/the-residents-of-town-x-participated-in-a-survey-t3186.html


P.S. Manhattan 上基本可以找到 Prep 所有问题的解答。