The residence of town X participated in a survey to study th

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The residence of town X participated in a survey to study the number of hours per week each resident spent watching TV.The distribution of the results of the survey had a mean of 21 hours and a standard deviation of hours.The number of hours that pat,a resident of town X watched TV 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 TV last week?30/B,20/C,18/D,12/E,6
请算出答案和过程说明思维路线.
在下十分感谢.

你题目漏打数字了.The distribution of the results of the survey had a mean of 21 hours and a standard deviation of____ hours.
我百度了一下,这里的数字应该是6.
建议你复习一下均值mean和标准差standard deviation的概念,
说这群人均值mean是21个小时,标准差是6小时,某人低于1-2个标准差,则是低于均值6-12个小时.因此这个范围就是21-12=9到21-6=15,也就是[9,15]这么一个范围,看选项,只有D中的12满足条件,选个D,结束.

英语翻译①：Residents of town X participated in a survey to determ 英译中 A study of the people in China's largest cities shows th 英语翻译According to a survey,with the greatdevelopment of econo there used to be a bridge in the west of the town,()? There used to be a church in the west of the town改反问 Is your primary residence in the state of Massachusetts?翻译? 英语翻译He was born in the German town of Bonn on the 16th of De i was born in a small mountain town,i moved to the city of L Bundanoon,a town in Australia,has decided to ban the sale of What's the best theater ( A of town B in city C in town D in Melksham is a small town in the south of England. This is a survey of the birthday of students in five classes