Somewhere, there may be a formula for this problem, but I don't know it . . .From a set of 12 flags, 4 blue,4 red, 2 green, 2 yellow,
how many types of 12-flag signals are possible?
Now what is the answer for 10-flag signals?
There are nine possible distributions of colors with ten flags: .
Now we find the number of each partition and add them.