MathDB
Pablo's list

Source: May Olympiad 2020 L1 P2

March 14, 2021
number theory

Problem Statement

Paul wrote the list of all four-digit numbers such that the hundreds digit is 55 and the tens digit is 77. For example, 15731573 and 75707570 are on Paul's list, but 27542754 and 571571 are not. Find the sum of all the numbers on Pablo's list. NoteNote. The numbers on Pablo's list cannot start with zero.