什么是季節(jié)變動(dòng)？研究它的意義何在？如何測定季節(jié)變動(dòng)？

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？（）

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

對(duì)某班級(jí)學(xué)生的生活狀況進(jìn)行統(tǒng)計(jì)調(diào)查，下列標(biāo)志中屬于不變標(biāo)志的是（）

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

一個(gè)地區(qū)一定時(shí)期的商品零售額屬于（）

A cumulative frequency polygon is also called （）.

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

品合格率指標(biāo)是（）

要了解某地區(qū)全部大學(xué)生的就業(yè)情況，那么（）