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Phone Number

Source: Indonesia Mathematics Olympiad 2006 Day 2 Problem 6

June 2, 2008
geometryprobabilitycombinatorics proposedcombinatorics

Problem Statement

Every phone number in an area consists of eight digits and starts with digit 8 8. Mr Edy, who has just moved to the area, apply for a new phone number. What is the chance that Mr Edy gets a phone number which consists of at most five different digits?