# Math Help - Number combinations ...

1. ## Number combinations ...

So... Let's say we have the numbers :

01 02 03 04 05
06 07 08 09 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25

If you need to choose 15 of them , I would like to know what's all the possible combinations .

2. How many ways to choose 15 out of 25 numbers?.

C(25,15)=3,268,760

3. well... ok, but how to use this formula ?

4. Most calculators do combinations. That's what I used to do this one.

The formula is $C(n,k)=\frac{n!}{(n-k)!k!}$

Do you know what a factorial is?. That's what the exclamation points are.

5. But I mean all possible combinations, without repeating them in a different order.