Back to the drawing board, Dad.

Lately R and I (Dad) have been playing with numbers - positive, negative, orders of magnitude, number lines, adding, and subtracting.

On the car ride home today R asked, "What is negative one thousand minus negative one thousand?"

D: Negative two thousand.
R: Whoa. Negative two thousand.
(Short pause here).
R: No, Dad. I mean SUBTRACT. What's negative one thousand subtract negative one thousand?
D (realizing he hadn't been paying careful enough attention): Do you mean what's negative one thousand - minus - negative one thousand?
R: Yeah!
D (smiling to himself): What do you think?
R: I think it's zero!
D: You're right, it's zero!
R (with obvious pleasure): Yeah!