of the
Week
|
|
Problem of the Week |
|
PROBLEM 255 This is the last problem for the semester (and the year). We'll return at the start of the spring semester. Merry Christmas * Feliz Navidad * Joyeux Noël * Frohe Weihnachten Each year ten couples meet for a Christmas dinner and an exchange of gifts. Each of the twenty people writes their name on a piece of paper and puts it into a hat. They take turns drawing names and give their gift to the person whose name they drew. If anyone draws either their own name or the name of their partner, everyone puts the name they have drawn back into the hat and everyone draws anew. How many different permissible drawings are there?For the math elves: a) What is the expected number of drawings before a permissible drawing is achieved? b) Same questions with n couples. You are visitor
number
2017
to this page. |