再给你一题,中英文都有:
Seven distinct pieces of candy are to be distributed among three bags. The red bag and the blue bag must each receive at least one piece of candy; the white bag may remain empty. How many arrangements are possible?
把 7 块不同的糖果分配到 3 个包中。要求红包和蓝包必须各分得至少一块糖果;白包可以为空。一共有多少种可能的分配方法?