2. 外语
  3. RESULTS ON A HISTORY TEST * Arithmetic mean The average (arithmetic mean) score for all of the students in the 3 classes is

RESULTS ON A HISTORY TEST * Arithmetic mean The average (arithmetic mean) score for all of the students in the 3 classes is

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问题 RESULTS ON A HISTORY TEST

*   Arithmetic mean
The average (arithmetic mean) score for all of the students in the 3 classes is
选项 A、less than 70
B、between 70 and 73
C、exactly 73
D、between 73 and 76
E、greater than 76
答案B
解析 本题的正确答案为(B)。本题若用式子(70+73+76)/3=73来计算平均值，将得到显然错误的结果；若采用计算公式(70×54+73×41+76×32)/(54+41+32)来求平均值，则显得比较麻烦；较为简便的方法是：先假设y的平均分73是三个班的平均分，然后比较x和z班分别比平均分高多少或低多少：x班全班比平均分总计低54×3=162分。z班全班比平均分总计高32×3=96分<162分。所以平均分应在70-73之间。
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