IMO Shortlist 1972 problem 6
Dodao/la:
arhiva2. travnja 2012. Show that for any

there exists a multiple of

not containing the digit

in its decimal expansion.
%V0
Show that for any $n \not \equiv 0 \pmod{10}$ there exists a multiple of $n$ not containing the digit $0$ in its decimal expansion.
Izvor: Međunarodna matematička olimpijada, shortlist 1972