将九件礼物分给五个人,其中三件完全相同,其余各不相同,且对每个人可获得的礼物数量没有限制。通过首先考虑分配不同礼物的方法数或其他方法,求分配这九件礼物的方案数。
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完整解法
6
1. Calculate the number of ways to distribute the 6 distinct gifts.
The number of distinct gifts is .
Since there are no restrictions, each of the distinct gifts can be given to any of the people.
Number of ways to distribute the distinct gifts = .
2. Calculate the number of ways to distribute the 3 identical gifts.
Since the gifts are identical, we only care about how many gifts each person receives. We can consider the possible groupings:
- All 3 gifts to 1 person: Choose person out of to receive all of them. This gives ways.
- 2 gifts to 1 person, 1 gift to another: Choose person to receive gifts ( ways), and of the remaining people to receive gift ( ways). This gives ways.
- 1 gift each to 3 different people: Choose people out of to receive gift each. This gives ways.
Total number of ways to distribute the identical gifts = .
(Alternatively, using the 'stars and bars' combinations with repetition formula: .)
3. Calculate the overall total number of ways to distribute all the gifts.
By the multiplication principle, the distinct and identical gifts can be distributed independently.
Total number of ways = .
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