Combinations without repetition

Find out how many different ways you can choose k items from n items set. With/without repetition, with/without order.

(n)
(k)

Calculation:

Ck(n)=(nk)=n!k!(nk)!  n=4 k=2  C2(4)=(42)=4!2!(42)!=4321=6

Number of combinations: 6