简答题 常用的长期趋势测定的方法有哪些？各有什么特点？

问答题时间序列构成因素有哪些？分解的基本原理和思路是什么？

问答题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？

单项选择题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？（）

A.80
B.200
C.20
D.100

单项选择题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？（）

A.80
B.0.40
C.155
D.75

单项选择题A cumulative frequency distribution would provide（）.

A.a graph of a frequency distribution
B.a running total of the frequencies in the classes
C.the proportion of the total frequencies which fall into each class
D.a very cloudy picture of the frequencies