You know the facts within 10, and that teen numbers are ten and some more. Put them together to add.
Key idea
Fill up a ten first. Break the other number into the part that makes 10 and the part that is left.
Why it works
Moving counters from one frame to the other does not change how many there are. And $10 + 3$ is easy: it is 13.
Worked example: Make a ten
What is $8 + 5$?
- 8 needs 2 to make 10.
- Break 5 into 2 and 3.
- $8 + 2 = 10$, and $10 + 3 = 13$.
Answer: 13
Worked example: Another one
What is $7 + 6$?
- 7 needs 3 to make 10.
- Break 6 into 3 and 3.
- $7 + 3 = 10$, and $10 + 3 = 13$.
Answer: 13
Worked example: Start with the 9
What is $5 + 9$?
- 9 needs only 1 to make 10.
- Break 5 into 1 and 4.
- $9 + 1 = 10$, and $10 + 4 = 14$.
Answer: 14
Common mistake
Breaking the second number the wrong way, so $8 + 5$ becomes $10 + 5$. But the 2 that made the ten came out of the 5! Only 3 are left: $10 + 3$.
For grown-ups: Use two egg cartons cut to 10 cups. Fill one first, then count what spills into the second.