TOT 402 1994 Spring O J4 ten coins in a circle
Source:
June 12, 2024
combinatorics
Problem Statement
Ten coins are placed in a circle, showing “heads” (the tails are down). Two moves are allowed:
(a) turn over four consecutively placed coins;
(b) turn over four coins placed as ( is one of the coins to be turned over, is not touched).
Is it possible to have all ten coins showing “tails” after a finite sequence of such moves? (A Tolpygo)