[Cobra]

You can get an inexpensive calculator that has the choose function on it. Look for a statistical calculator that has an nCr function key. The formula given in the other post was correct N!/((N-r)!*r!) were ! means factorial, this can also be found on many calculators.

Let me give you two examples and you will see how to figure the answer out if you do not have a calculator with these functions on them.

(52 choose 3) the number of unique flops=
52!/((52-3)!*3!) this simplifies to 52*51*50/1*2*3=22100
You start at 52 and go backwards a total of three terms then divide by 1 and go forward a total of three terms.

(52 choose 5)=52!/(47!*5!) this simplifies to 52*51*50*49*48/1*2*3*4*5 = 2598960 you notice that the top has five terms starting at 52 and the bottom has five terms starting at 1.

Cobra