對全國各鐵路交通樞紐的貨運量、貨物種類等進行調查，以了解全國鐵路貨運概況。這種調查屬于（）

某廠某年職工勞動生產率為20000元，是歷史最高水平的1.2倍。這里的1.2倍是（）

A cumulative frequency polygon is also called （）.

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？（）

Which of the following is not the goal of descriptive statistics?（）

One advantage of a stem and leaf plot over a frequency distribution is that （）.

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（）

品合格率指標是（）

If data are grouped into intervals and the number of items in each group is listed, this could be called a （）

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？