O.2 Find related addition facts - sums up to 20
What is addition?
Addition means putting numbers together to find how many there are in all. The answer to an addition problem is called the sum.
- 2 + 3 = 5
- 7 + 1 = 8
- 10 + 4 = 14
When you add, you are finding the total number of objects.
What are related addition facts?
Related addition facts are addition problems that use the same numbers but may be in a different order. These facts help you solve problems faster.
- 3 + 5 = 8
- 5 + 3 = 8
Related facts have the same sum, even when the numbers switch places.
Adding numbers in any order
You can add numbers in any order and still get the same sum. This is called the commutative property of addition.
- 4 + 6 = 10
- 6 + 4 = 10
Switching the order of numbers does not change the answer.
Finding sums up to 20
First graders add numbers with sums up to 20. Using related facts can make adding easier and quicker.
- 9 + 6 = 15
- 6 + 9 = 15
- 12 + 7 = 19
If one addition fact is easy, its related fact will be easy too.
Using related facts to help you add
You can use addition facts you already know to help solve new problems. This strategy helps you add within 20 more confidently.
- If you know 5 + 5 = 10, then 5 + 6 = 11
- If you know 8 + 2 = 10, then 8 + 3 = 11
Think about facts you already know to help with harder ones.
Common Core alignment: CCSS.MATH.CONTENT.1.OA.C.6 – Add within 20, demonstrating fluency for addition within 10.
Notes for teachers
This free lesson is aligned with CCSS.MATH.CONTENT.1.OA.C.6. Use it for whole-class instruction, independent practice, or homework.
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