Method One
Your calculator might be able to do this. Mine does it like this.
6
nCr
2
=
15
Method 2
You could simply set up 6C2
This gives you
[tex] \frac{n!}{(n- r)! r!} = \frac{6!}{(6 - 2)!2!} = \frac{6!}{4! 2!} = \frac{6*5}{2*1} = 15 [/tex]
Method Three
You only have to do this a couple of times to see how the cancellation works.
[tex] \frac{6!}{4!2!} = \frac{6*5*\st{4*3*2*1}}{4*3*2*1 * 2*1} [/tex]
After all the cancellation takes place you have
6*5/2 = 15
