A pizza restaurant lets you make your own pizza. You have a choice between: 3 doughs (pick 1) 10 toppings (pick exactly 2, you can't selected the same topping twice). Chris is a food critic and he eats at this place frequently. He orders exactly one of these "make your own" pizzas every time and numbers them in his notes. The first one he ever ate is #1, the second one is #2, etc. At what pizza number is it unavoidable that he will eat one kind of pizza for the third time? 2*3*10*9+1 2*3*10*9/2+1 3*3*10*9 3*3*10*9/2 QUESTION 13 This is an extra credit question. If A is a set with n elements, and B is a set with m elements, and m>n, and if a function from A to B is selected randomly (with all functions being equally likely), what is the probability that the function will be injective? m!-n! m"- m! n! m" -n m! (m-n)!nm m-n n(m+n) m! n! (m+n) m! (m-n)!m"