有道数学向大家求助~~

美小波

110. 11364-!-item-!-187;#058&007646

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?



(A) 30

(B) 20

(C) 18

(D) 12

(E) 6

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【答案】 D

【思路】 平均數與標準差的概念

題目的數據: 平均數(mean) :21 hrs  標準差(standard deviation) : 6 hrs



由Pat 上星期看電視的時間在1~2個標準差之下可得知(between 1 and 2 standard deviations below the mean)，時間範圍應該坐落在9hrs~15hrs之間 è 答案D 符合算出來的要求

即使这里有解答。。。但我还是没能弄明白到底是怎么出来这个答案的。

谢谢各位了~~~~~~~

genius_fang

PAT看电视的时间比中位数小移到两个方差，也就是21-6~21-12，所以就是15~9.这道题目其实和方差中位数没什么关系，只是用到这两个名词~

美小波

谢谢你的回答~~  真是及时雨啊~~！！

美小波

谢谢你的回答！！