✔ 最佳答案
6a)4^5 = 1024 waysb)3^5 = 243 ways
7a)6! = 720 ways
b)Consider 3 specific persons as 1 element.
There are 4 elements.
3! * 4! = 144 ways
c)Arrange other 4 persons first ,
For example : ( ) 1 ( ) 2 ( ) 3 ( ) 4 ( )
4! ways , then insert 2 specific persons to any two ( ) among 5 brackets ,
5P2 ways ,
4! * 5P2 = 480 ways.
Alternative :
All ways - 2 specific persons following each other ways
= 6! - 2!*5! = 480 ways
8a)6 * 6 * 5 = 180 waysAlternative :
7P3 - 6P2 = 180 ways
b)5 * 5 * 4 * 3! = 600 waysAlternative :
(3P1) (6! - 5!) = 600 ways
c)Case 1 :
34X : 5 ways
35X : 5 ways
36X : 5 waysCase 2 :
4XX : 6P2 ways
5XX : 6P2 ways
6XX : 6P2 waysTotal (5 + 6P2) * 3 = 105 are greater than 330.
2011-01-16 23:44:55 補充：
8b) Corrections :
5 * 5 * 3 = 75 ways
Alternative :
3 * (6P2 - 5P1) = 75 ways
Sorry!
2011-01-19 13:33:55 補充：
個位可以是 1 , 3 , 5 ,
3 ways
選定個位後剩下 6 個數,0 不能是百位
So 百位 5 ways
最後剩下 5 個數
十位 5 ways
Total 3*5*5 = 75 ways.
