企业生产一种产品需顺次经过四个车间，这四个车间的废品率分别为1.5%、2.0%、2.0%和1.0%。该企业生产这种产品的平均废品率是多少？

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

Which of the following statements is not true？（）

Claudia Taylor, Director of Global Industrial Sales in Melbourne, is concerned by a deteriorating sales trend. Specifically, the number of customers is stable at 1500 but they are purchasing less each year. She orders her staff to search for causes of the downward trend by selecting a focus group of 40 industrial customers. For this study, the set of 40 industrial customers is a （）.

品合格率指标是（）

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

以2000年a0为最初水平，2016年an为最末水平，计算钢产量的年平均发展速度时，须开（）

对全国各铁路交通枢纽的货运量、货物种类等进行调查，以了解全国铁路货运概况。这种调查属于（）

A cumulative frequency polygon is also called （）.