问答题 为什么在计算平均指标的基础上还有必要进一步计算变异指标？

单项选择题 The number of phone calls arriving at a switchboard each hour has been recorded and the following frequency distribution has been developed. What is the approximate range of the number of phone calls arriving each hour？（）

单项选择题 The number of phone calls arriving at a switchboard each hour has been recorded and the following frequency distribution has been developed. What is the cumulative frequency of the third class？（）