Adding Three Small Numbers
Add three one-digit numbers using strategies including looking for pairs that make 10
What a learner can do afterwards
- Calculate 5 + 7 + 3 by first adding 7 + 3 = 10, then 5 + 10 = 15
- Add any three single-digit numbers correctly
- Identify useful pairs within three addends to make the calculation easier
1 · Read
When you add three numbers, you can add them in any order. Look for two numbers that make 10. Add those two first. Then add the last number to 10. This turns a hard sum into an easy one.
Leo has 4 blocks, 6 blocks, and 8 blocks. He looks for a pair that makes 10 first. 4 and 6 make 10. Then he adds 8 more. 10 + 8 = 18. Leo has 18 blocks.
You can add numbers in any order. The total stays the same. Always look for a pair that makes 10 first. It makes adding three numbers much easier.
Find two numbers that make 10, add them first, then add the last number.
More to read
2: Addition
Adding three numbers is easy if you spot a pair that makes 10. For 5 + 7 + 3, notice 7 + 3 is 10. Then add 5 to get 15. Looking for pairs first saves effort. Ten is a friendly number that is quick to add.
Properties of addition
Order does not matter in addition. You can add any two first. Pick the pair that is simplest. Doubles and tens are good picks. Then add the last number. Trying a new order often turns hard sums into easy ones.
Visualizing the Commutative Property of Addition
Seeing addition move helps. Blocks can slide together in any order. 2 + 3 + 5 still makes 10 however you group it. Draw arcs to show which two you added first. Your drawing proves your clever choice.
Explore more
2 · Watch
En anglaisTake it off screen
Where it sits
Learn first
Optional connections
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
17 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.