BdMO Online Forum

A four headed monster has 63 children . He wants to give each child a name of three English letters . And every 63 names will be different . In a name of a child , a letter can be used more than once . What is the minimum number of letters does the monster need to use ?

The answer is 4 letters

@Thanic nur Samin, Please practise posting full solutions or at least hints for your solution unless asked explicitly for just the answer to the problem. Because most often, people asking for help are actually asking for ideas/keys to solve the problem and not just the answer.

Here's a possible way to solve this problem.