Problem

Source: Indonesia IMO 2010 TST, Stage 1, Test 5, Problem 4

Tags: combinatorics proposed, combinatorics



Prove that the number $ (\underbrace{9999 \dots 99}_{2005}) ^{2009}$ can be obtained by erasing some digits of $ (\underbrace{9999 \dots 99}_{2008}) ^{2009}$ (both in decimal representation). Yudi Satria, Jakarta