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？

A summary measure that is computed from a sample to describe a characteristic of the population is called（）

在组距数列中，下限就是（）

The number of class intervals in a frequency distribution is usually between （）.

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 （）.

要了解某地区全部大学生的就业情况，那么（）

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？

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（）

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？（）