It is known that these twelve students are from three different schools. There are 4 students from school A, 5 students from school B and 3 students from school C.
Assume that students from the same school are not distinguished from each other. Find the number of ways in which:
1) the twelve students line up in a row.
2)the twelve students line up in a row such that the the 3 students from school C are next to each other.
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2009-12-03 7:17 am
回答 (1)
2009-12-03 9:34 am
✔ 最佳答案
1)the twelve students line up in a row.12! / (4! 5! 3!)
= 27720 ways
2) Let the 3 students from school C is one element :
Then total 4 + 5 + 1 = 10 elements
10! / (4! 5! 1!)
=1260 ways
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