请教解数学题。

来源: 于 2010-09-06 18:14:36 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

We have 20 thousand dollars that must be invested among 4 possible opportunities. Each investment must be integral in units of 1 thousand dollars.
How many different investment strategies are possible?
What if not all money need be invested?