Finding a missing number in addition
Understand subtraction as finding an unknown addend (e.g. 10 − 8 = ? is the same as 8 + ? = 10)
What a learner can do afterwards
- Solve 10 − 8 by thinking 'what do I add to 8 to make 10?'
- Explain that subtraction can be thought of as a missing-addend problem
- Use known addition facts to solve related subtraction problems
1 · Read
When you see a subtraction problem like 10 − 8 = ?, you can turn it into an addition question instead. Ask yourself: what number do I add to 8 to reach 10?
Mia has 8 crayons. She wants 10 crayons. She thinks: 8 + ? = 10. She counts up 2 more, so she needs 2 more crayons. That means 10 − 8 = 2.
You already know your addition facts. Use them backwards! If you know 6 + 4 = 10, then you also know 10 − 6 = 4 and 10 − 4 = 6.
10 − 8 = ? is the same question as 8 + ? = 10, so your addition facts can solve subtraction too.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
18 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.