数学题，你能给初中生解释清楚这道题的解答吗？

来源: 于 2010-04-17 20:01:57 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

这是Mathcounts的题，关键是怎样向初中生解释清楚这道题的解答。

A bag contains three blue, four red, and five green marbles. The marbles are to be arranged into three rows so that at least one marble is in each row. In how many difference ways can the marbles be arranged?