Idea 12of 23Builds onBuild a number more than one way
Add in any order
Does the order of two numbers matter when you add?
Today you'll discover
- what swapping the numbers does
- why the total stays the same
- why subtraction is different
Think first3 400 and 25 000, end to end
Is 3 400 + 25 000 the same as 25 000 + 3 400?
Decide first, then press Next. Compare the lengths of the two bars.
A bar split into a short piece of 3 400 and a long piece of 25 000, with a bracket over the whole marked total, a question mark. A second bar under it holds the same pieces the other way round, sliding into place. Then the sentences 3 400 + 25 000 = 28 400 and 25 000 + 3 400 = 28 400. The last step shows 18 600 and 4 250.
See the whole ideathe big idea and the key word, in one place
The big idea
You can add two numbers in either order: the total stays the same.
For exampleStart with the bigger number to count on: 25 000 + 3 400 is easier to do in your head than 3 400 + 25 000.
Key word
- commutative property
- adding two numbers in either order gives the same total: a + b = b + a
Ready to use it?
- Change the order of an addition to make it easier.