回复：请教解数学题。
guest1000
2010-09-07 20:04:56
( reads)
Here is the easiest way to solve the problem.
Put all 20 balls on a line. There are 19 positions between these 20 balls. If you want to put them in 4 bins without any bin being empty, the number of possibilities is (19 choose 3).
Done.