How many cards can Nils show you without revealing his 8-digit number?
Source: Norwegian Mathematical Olympiad 2017 - Abel Competition p3a
September 3, 2019
combinatoricsnumber theoryDigits
Problem Statement
Nils has a telephone number with eight different digits.
He has made cards with statements of the type “The digit occurs earlier than the digit in my telephone number” – one for each pair of digits appearing in his number.
How many cards can Nils show you without revealing his number?