Stage 3 · Structure / #16
Why Subtracting a Negative Means Adding
Coming soon
The video is in production. Follow along on GitHub to hear when it is out.
The idea
Subtraction asks how far apart two numbers are: how many steps on the number line from the number you subtract to the one you start with. Negative two is left of zero, so from negative two to three is five steps, and three minus negative two is five.
A common mix-up
Three minus negative two is one: three minus two is one, and the minus sign doesn't matter.
Where it stops working
One is really three plus negative two: from three, two steps to the left, landing on one. That's adding a negative, not subtracting one.
School year
China 7 US 6