1) How many combinations exist of the letters W, X, Y, Z, taking two at a time?
2)A workman has six jobs to do. In how many different orders can he do them?
1.) There is 12 combinations.
2.) He can do his six jobs in 15 different orders.
Also, if you need to solve questions like this that don't have very large numbers, try writing down every combination you could think of until you are sure you've gotten all of them.
Hope this helped! :)