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 9−3=69 - 3 = 6.
Since there are no restrictions, each of the 66 distinct gifts can be given to any of the 55 people.
Number of ways to distribute the distinct gifts = 56=156255^6 = 15625.

2. Calculate the number of ways to distribute the 3 identical gifts.

Since the 33 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 11 person out of 55 to receive all of them. This gives (51)=5\binom{5}{1} = 5 ways.
  • 2 gifts to 1 person, 1 gift to another: Choose 11 person to receive 22 gifts (55 ways), and 11 of the remaining 44 people to receive 11 gift (44 ways). This gives 5×4=205 \times 4 = 20 ways.
  • 1 gift each to 3 different people: Choose 33 people out of 55 to receive 11 gift each. This gives (53)=10\binom{5}{3} = 10 ways.

Total number of ways to distribute the identical gifts = 5+20+10=355 + 20 + 10 = 35.

(Alternatively, using the 'stars and bars' combinations with repetition formula: (3+5−15−1)=(74)=35\binom{3+5-1}{5-1} = \binom{7}{4} = 35.)

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 = 15625×35=54687515625 \times 35 = 546875.

答案

546875546875

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