Mr. Murgatroyd decides to throw his class a pizza party, but he’s going to make them hunt for it first. He chooses eleven locations in the school, which we’ll call 1,2, \ldots, 11. His plan is to tell students to start at location 1 , and at each location n from 1 to 10 , they will find a message directing them to go to location n+1; at location 11, there’s pizza!
Mr. Murgatroyd sends his teaching assistant to post the ten messages in locations 1 to 10. Unfortunately, the assistant jumbles up the message cards at random before posting them. If the students begin at location 1 as planned and follow the directions at each location, show that they will still get to the pizza.