There are six combinations of two colors: red yellow, red blue, yellow blue, yellow red, blue yellow and blue red.
There are six combinations of three colors: red, yellow, blue, red, blue, yellow, Huang Honglan, yellow, blue, red, blue, red and yellow.
So there are: 3+6+6= 15 kinds in total.
1. How to write a model essay for the summer vacation plan
First of all, the timetable
1. Four "1 hour guarantees" per day.