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51ab, a1b9 4-digit numbers wanted

Source: XIII May Olympiad (Olimpiada de Mayo) 2007 L1 P2

September 22, 2022
number theoryDigits

Problem Statement

Let X=a1b9X= a1b9 and Yab=51abY ab = 51ab be two positive integers where aa and bb are digits. XX is known to be multiple of a positive two-digit number nn and YY is the next multiple of that number nn. Find the number nn and the digits aa and bb. Justify why there are no other possibilities.