Problem 15

A magician has 13 unique cards. He places them down infront of you in a row.
(i) In how many ways can he do this?
(ii) The magician then asks you, in how many different sets of 7 cards that he can select from the 13 unique cards.
(iii) Given that he now has n cards, can you derive a general formula for (i) and (ii) (given that he wishes to select k cards in ii).