this is the full question :
How many signals can be made with 3 white, 3 green, and 2 blue flags by arranging them on a mast:
a). all at a time.
b). three at a time
c). 5 at a time.
a). 3+3+2=8 flag at a time. The answer is : 8!/3!3!2!, because there are flags that has the same color.
b). this is tricky. If there are 3 blue flags, to arrange the signal is simple: 3.3.3=27 ways, but if 2 flags, confusing. The answer is 26, so i assumed it's from 27 - 1 where :
* 27 is when there are 3 blue flags
* 1 is when all the blue is used on the mast..
how to do it without subtracting ?