2. 外语
  3. From a set of 100 numbers, half were selected to form group I, and 60 percent of the remaining numbers were selected to form gro

From a set of 100 numbers, half were selected to form group I, and 60 percent of the remaining numbers were selected to form gro

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问题 From a set of 100 numbers, half were selected to form group I, and 60 percent of the remaining numbers were selected to form group II. The average (arithmetic mean) of the numbers ingroup I is 24.4, and the average of the numbers in group II is 31.5. Which of the following is closestto the average of the numbers in groups I and II combined?
选项 A、27.1
B、27.6
C、27.8
D、28.0
E、28.3
答案A
解析 确定I中个数为100/2=50，确定Ⅱ中个数为(100-50)×60％=30，则平均值：(24-4×50+31.5×30)/(50+30)=27.0625，与A选项最接近。
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