# Difference between revisions of "2014 UNM-PNM Statewide High School Mathematics Contest II Problems/Problem 5"

## Problem

$5^n$ is written on the blackboard. The sum of its digits is calculated. Then the sum of the digits of the result is calculated and so on until we have a single digit. If $n = 2014$, what is this digit?

## Solution

This problem needs a solution. If you have a solution for it, please help us out by adding it. What you have to realize is that the sum of the digits of a number is the number $\pmod{9}$. We can prove this right now.