變量數列中，各組頻率之和應（）

If the individual class frequency is divided by the total frequency, the result is the （）.

對某班級學生的生活狀況進行統計調查，下列標志中屬于不變標志的是（）

Simon Arnett, Director of Human Resources, is exploring the causes of employee absenteeism at Buderim Bottling during the last operating year (1 January 2005 to 31 December 2005). Personnel records of 50 employees are selected for analysis. (The plant employs 250.) For this study, the average number days absent for these 50 employees is a （）.

One rule that must always be followed in constructing frequency distributions is that （）.

某企業(yè)的生產計劃完成百分比采用如下分組，請指出哪項是正確的（）

某班的學習按考試成績分為60分以下，60-70，70-80，80-90，90-100，這種分組（）

A summary measure that is computed from a sample to describe a characteristic of the population is called（）

為什么在計算平均指標的基礎上還有必要進一步計算變異指標？

企業(yè)生產一種產品需順次經過四個車間，這四個車間的廢品率分別為1.5%、2.0%、2.0%和1.0%。該企業(yè)生產這種產品的平均廢品率是多少？