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 （）.

A cumulative frequency distribution would provide（）.

一个地区一定时期的商品零售额属于（）

A cumulative frequency polygon is also called （）.

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). The average number of absences per employee, calculated from the personnel data of all employees, is a （）.

要了解某地区全部大学生的就业情况，那么（）

变量数列中，各组频率之和应（）

某班的学习按考试成绩分为60分以下，60-70，70-80，80-90，90-100，这种分组（）

常用的长期趋势测定的方法有哪些？各有什么特点？

如果居民按报告期价格购买商品需多支出40万元，报告期商品销售额为200万元，则价格指数为（）