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？（）

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

如果居民按報告期價格購買商品需多支出40萬元，報告期商品銷售額為200萬元，則價格指數(shù)為（）

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

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

要了解某地區(qū)全部大學生的就業(yè)情況，那么（）

最能反映離散程度的指標是（）

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

A cumulative frequency polygon is also called （）.

一個地區(qū)一定時期的商品零售額屬于（）