Having survived the zombie apocalypse of last week, you are sending auntie Lucinda a card to let her know you are sort of OK. You have a limited supply of hugs and kisses: two O’s and three X’s. You will send her at least two. If the order does not matter—XXO and OXX would be considered the same—how many possible combinations do you have to choose from?
Submit your answer to Gene Wirchenko <firstname.lastname@example.org>. Your answer should be in the form of a proof. That means to show how your answer must be correct. The deadline is Wednesday, November 15, 2017 at noon Pacific Time. I will post the answer shortly after.