Transcript

NARRATOR:

Let's see how traveling in a lift ties in with adding and subtracting negative numbers. Suppose I come in at floor 2 and want to go up to floor 5. How many floors do I go up? Pretty clearly, that's 3. And that can be worked out by doing the calculation 5 subtract 2 equals 3.

Now, suppose I come in at floor minus 3, and I want to go up to floor 4. How many floors do I have to go up? You can work it out looking at the lift buttons. Going up 3 floors, gets us to floor 0 and another 4 floors get us to floor 4.

So that's 7 floors we've gone up all together. So that suggests using the same calculation as before that we would say 4 subtract minus 3 equals 7. You'll explore the mathematical rules we can use to work this out next.