Hehe... smart man.
Another one is that
1 / 3 * 3 = 1
<==> 0.333... * 3 = 1
<==> 0.999... = 1
"yes but 1/3 does not equal .333... it's just an approximation since there's no perfect way to represent 1/3"
If 1/3 doesn't equal .333... then how much do they differ by?
Me: 0.9999... is not the same as 1
Him: Well if it's not the same is it more than 1 or less than 1?
Me: Less
Him: Okay then how much less is it?
At this point I started trying to do 1 - 0.999..., using the methods I'd been taught, and after a few iterations of "borrowing" the 1 I realized the answer was 0.000... which I was pretty convinced was equal to 0.