19 cards and divisibility by 11
Source: All-Russian MO Round 4, 2005
April 2, 2005
combinatorics proposedcombinatorics
Problem Statement
9.2 Given 19 cards. Is it possible to write a nonzero digit on each card in such a way that you can compose from these cards an unique 19-digits number, which is divisible by 11?
(R. Zhenodarov, I. Bogdanov)