Back in school our first lessons in calculus were with (imagined) oranges. You know, the kind of "If you have 7 oranges, and you get 5 more, how many do you have?"

Maybe you should try to use those with your kid when you stimulate him to find it out. People learn best when they actually have to do things. Letting your kid gain insight in this way would be better than just saying "Well, I'm right and you're wrong!"

So buy a bag of oranges (or whatever currency you want to use), give him fourteen and then ask him to give you 27 oranges back. Try the opposite situation (27 -14), and try a few other combinations. I think that that would be the best way to make him understand. Or maybe you find out that he is right - that's the beauty of experimenting :-)

Whymme