weights and stones
Source: Saint Petersburg MO 2020 Grade 10 Problem 1
May 7, 2020
combinatorics
Problem Statement
Andryusha has stones of different weight and he can distinguish the stones by appearance, but does not know their weight. Every evening, Andryusha can put exactly stones on the table and at night the brownie will order them in increasing weight. But, if the drum also lives in the house then surely he will in the morning change the places of some stones.Andryusha knows all about this but does not know if there is a drum in his house. Can he find out?