Peter is looking for an 8 digit phone number with the following conditions :
(1) First digit must be 9, 6 or 5.
(2) Number repitition is allowed.
(3) There is only 3 '8's and always next to each other (i.e. 888).
How many phone numbers are there?
Please show steps.
Permutation & Combination
2013-12-10 3:40 pm
回答 (1)
2013-12-10 8:56 pm
✔ 最佳答案
First digit 3 possible ways(9,6,5)remain 7 digit it must has 3 "888" only has 5 possible ways.
(1234567 =>123, 234,345,456,567)
and then remain 4 digit only can fill by (0 to 9 except 8), so 9*9*9*9 possible ways,
Therefore, the answer would be :
3*5*9*9*9*9 =98415
收錄日期: 2021-04-13 19:50:49
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20131210000051KK00030