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（）

常用的长期趋势测定的方法有哪些？各有什么特点？

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 （）.

Descriptive statistics deals with methods of（）

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

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

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？（）

Simon Arnett, Director of Human Resources, is exploring the causes of employee absenteeism at Buderim Bottling during the last operating year (1 January 2005 to 31 December 2005). Personnel records of 50 employees are selected for analysis. (The plant employs 250.) For this study, the average number days absent for these 50 employees is a （）.

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

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？（）