Permutation
2010-12-11 8:18 pm
Six letters A,B,C,D,E and F to be arranged in a row, how many arrangement can be made if A,B and C must be separated from each other?
回答 (1)
2010-12-11 8:31 pm
✔ 最佳答案
Step 1 :Arrange D , E and F first :3! = 6 waysExample :D , E , F
F , D , E
D , F , E ......
Step 2 :Insert A , B , C into 3 out of 4 gaps between D , E , F :Example :( ) D ( ) E ( ) F ( ) =========> 4 gapsExamples of possible cases :(A) D (B) E ( ) F (C)( ) D (C) E (A) F (B)............................4P3 waysAnswer is (4P3) (3!) = 144 ways
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https://hk.answers.yahoo.com/question/index?qid=20101211000051KK00517