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？（）

常用的長期趨勢測定的方法有哪些？各有什么特點？

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（）

Which of the following is best to show the percentage of a total budget that is spent on each category of items？（）

The number of class intervals in a frequency distribution is usually between （）.

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

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

A student achieves an 82 on the first test in a statistics course. From this, she assumes that her average at the end of the semester (after other tests) will be about 82. This is an example of （）.

一個地區(qū)一定時期的商品零售額屬于（）

在組距數(shù)列中，下限就是（）