sum of digits of 3n if sum of digits of n is 100 and of 4n is 800
Source: 2020 Dürer Math Competition Finals Day2 E4 https://artofproblemsolving.com/community/c1622639_2020_
January 7, 2022
sum of digitsnumber theory
Problem Statement
We have a positive integer , whose sum of digits is . If the sum of digits of is then what is the sum of digits of ?