Maximum number of phone numbers in a company
Source: Moldova NMO 2002 grade 8 problem nr.4
November 2, 2008
Problem Statement
All the internal phone numbers in a certain company have four digits. The director wants the phone numbers of the administration offices to consist of digits , , only, and that any of these phone numbers coincide in at most one position. What is the maximum number of distinct phone numbers that these offices can have ?