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请教 PREP里的数学题4-4
The residents of Town X participated in a survey to determine 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 6 hours. The number of hours that Pat, a resident of Town X, watched TV last week was between 1 and 2 standard deviation below the mean. Which of the following could be the number of hours that Pat watched TV last week?
30
20
18
12
6
(题目没有打错) |
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