MathDB
Chef Kao cut a pizza into 2k pieces

Source: 2022 Thailand Online MO P6

April 4, 2022
combinatorics

Problem Statement

Let nn and kk be positive integers. Chef Kao cuts a circular pizza through kk diameters, dividing the pizza into 2k2k equal pieces. Then, he dresses the pizza with nn toppings. For each topping, he chooses kk consecutive pieces of pizza and puts that topping on all of the chosen pieces. Then, for each piece of pizza, Chef Kao counts the number of distinct toppings on it, yielding 2k2k numbers. Among these numbers, let mm and MM being the minimum and maximum, respectively. Prove that m+M=nm + M = n.