2. 职称英语
  3. Closing prices for a certain stock were recorded each day for a week in the tabl

Closing prices for a certain stock were recorded each day for a week in the tabl

游客2025-02-27  10
问题 Closing prices for a certain stock were recorded each day for a week in the table above. If the monthly average (arithmetic mean) was 18.43 and the standard deviation was 0.27, how many days during this week did the closing price fall within two standard deviations from the average?
选项 A、1
B、2
C、3
D、4
E、5
答案 C
解析 Since two standard deviations away from the mean works out to 18.43-0.27×2=17.89, there are 3 days during which the stock prices fell between 17.89 and 18.43: Monday, Tuesday, and Wednesday. We really don’t have to worry about prices above the mean, because there were none of them during this time frame.
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