1. There are 9 different dolls. The dolls are distributed among 3 children.
In how many ways can the dolls be distributed if the children get the
same number of dolls?
2. Find the number of ways arranging 2 boy scouts and 3 girl guides in a
row if
(a)there is no restriction
(b)no boy scouts can stand together.
Combination and Permutation
2011-01-19 5:18 am
回答 (3)
2011-01-19 5:43 am
✔ 最佳答案
1 First, the no. of ways to distributed 9 different dolls into 3 groups is 9!/(3!3!3!). Then since the dolls in each group is different and will give different feeling to the children. So the arrangement scheme of the dolls is important. no. of ways is just [9!/(3!3!3!)](3!) = 100802(a) 5! = 120 (b) First, arrange the girl scouts in a line with 3! = 6 ways. Then arrange two boy scouts among the 5 holes. Total no. of ways = (3!)(5C2) = 60 ways 2011-01-18 22:15:15 補充：
2(b) Total no. of ways = (3!)(4P2) = 72 ways
2011-01-19 6:06 am
我都係禁想
3!*4*3
=72
我答案啱唔啱?
3!*4*3
=72
我答案啱唔啱?
2011-01-19 5:55 am
myisland...點解第一題臨尾要乘番3!??
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