1. There are four colors of water: red, yellow, blue, and white. Now pour them into three cups without mixing. How many ways are there to pour them?


1. Three cups can all be filled with water of the same color, can be filled with water of two different colors, and can also be filled with water of three different colors. The total number of ways to pour water is exactly equal to the number of combinations of taking 3 elements from 4 different elements with repetition allowed, which is $C_{3+4-1}^{3}=C_{6}^{3}=20$ (ways).