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?

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.

Oh my, I hadn’t listened in a while. Your older son’s voice has changed a lot!