I still remember my teacher bitching me out in front of the class when we were learning negative numbers because when he asked me how I figured out the correct answer I said that the positive numbers and negatives cancelled each other out. Like -4 and positive 5, the negative 4 cancels out 4 on the positive side and you are left with 1. Maybe that wasn't the correct verbiage but it gave me the correct answer every time. He was a dick about correcting me though.