MathDB
Israel 2011 Q5 - Process with two lists

Source: Israel National Olympiad 2011 Q5

August 8, 2019
combinatoricsnumber theoryProcesses

Problem Statement

We have two lists of numbers: One initially containing 1,6,11,...,96, and the other initially containing 4,9,14,...,99. In every turn, we erase two numbers from one of the lists, and write 13\frac{1}{3} of their sum (not necessarily an integer) in the other list. We continue this process until there are no possible moves.
[*] Prove that at the end of the process, there is exactly one number in each list. [*] Prove that those two numbers are not equal.