Trying out Edmund Harriss’s puzzle with kids

Saw a neat puzzle posted by Edmund Harriss last night:

Quick puzzle: Take two sets of numbers so that the sum of any two in either (allowing repeats) is in the other. If 1 is in one of the sets must they share a number?

— Edmund Harriss (@Gelada) August 21, 2018

I thought it would be fun to try it out with the boys this afternoon.

I didn’t give them much direction after introducing the puzzle – just enough to make sure that my younger son understood the situation:

After the first 5 minutes they had the main idea needed to solve the puzzle. In this video they got to the solution and were able to explain why their solution worked:

Definitely a fun challenge problem to share with kids. You really just have to be sure that they understand the set up and they can go all the way from there.