# How to Find Number Combinations

• 1). Determine the size of the pool of numbers from which you will pick your combination. This value is "n" in the combination equation. For example, if you wanted to know how many combinations you could pick from a pool of five distinct numbers (such as 1,2,3,4 and 5), your value of n would be 5.

• 2). Determine the quantity of numbers which you want in each combination. This value is "r" in the combination equation. In the example, you might want to find the number of unique combinations which can be made by taking samples of two numbers out of the pool of five, so r would be 2.

• 3). Calculate the quantity of unique combinations of r numbers out of the pool of n numbers, using the following equation; C = n!/[(n-r)!r!]. The symbol "!" means that you are to take the factorial of the preceding number, where a factorial of some number x is equal to (x)(x-1)(x-2)(x-3) ... (1). In the example, the unique combinations of two numbers out of five would equal 5!/[(5-2)!2!] = 120/12 = 10.