Depth 1 · 32 s
How far apart
Twelve take away five leaves seven - and seven and twelve are five apart. Subtracting finds what's left or the difference, undoes adding, and unlike adding, its order matters.
About this video
Subtracting answers two questions that sound different but are the same sum. The first is how many are left: twelve dots, five of them taken away, seven left, so 12 - 5 = 7. The second is how far apart two numbers are: put 7 and 12 on the number line and count up from 7, and you make five hops to reach 12. That gap is called the difference.
You can always check a subtraction by adding: 7 + 5 = 12, so 12 - 5 = 7. Subtracting undoes adding. But there is one way subtracting is not like adding. When you add, the order doesn't matter. When you subtract, it does. 7 - 3 is 4, three hops to the left from 7. 3 - 7 is seven hops to the left from 3, which takes you past zero to -4. This short animation shows all three ideas on dots and on the number line, and goes with the Taking Away, and How Far Apart lesson of Numbers Level 1 on Knaph.
This video shows depth 1 of Subtraction.
Learn SubtractionTranscript
- 0:00Twelve dots. Take five away. What's left?
- 0:04Five go, and seven are left.
- 0:09Or ask how far apart seven and twelve are. Count up from seven. Five hops.
- 0:15Check it by adding. Seven and five is twelve. Subtracting undoes adding.
- 0:20But the order matters. Seven take away three is four. Three take away seven goes below zero.
- 0:27Subtracting tells you what's left, or how far apart.