Addition Facts Within 20

Adding numbers is fun and easy when you know a few secret tricks! When we add numbers and the answer is between $11$ and $20$, we call these addition facts within 20.

Here are three great strategies to help you solve these problems quickly.

1. Making a Ten

The number $10$ is a very friendly number in math. When adding, try to turn one of the numbers into a $10$ first!

Example: $8 + 5 = ?$

• Start with the bigger number: $8$.
• How many more do you need to make $10$? You need $2$.
• Take that $2$ away from the $5$. (Since $5 = 2 + 3$, you have $3$ left over).
• Now you have $10 + 3$, which is much easier to add!
• $8 + 5 = 8 + 2 + 3 = 13$

2. Using Doubles

Doubles are when you add the exact same number to itself. Memorizing your doubles makes math much faster!

Examples of Doubles:

• $5 + 5 = 10$
• $6 + 6 = 12$
• $7 + 7 = 14$
• $8 + 8 = 16$

3. Near Doubles

If the two numbers you are adding are almost the same, you can use a double to help you find the answer.

Example: $6 + 7 = ?$

• We know that $6$ and $7$ are right next to each other.
• Think of the double you already know: $6 + 6 = 12$.
• Because $7$ is just one more than $6$, you just add $1$ to your double's answer.
• $12 + 1 = 13$
• So, $6 + 7 = 13$

Let's Practice!

Try using these strategies on these problems:

• $8 + 7 = ?$

  • Try Near Doubles: $7 + 7 = 14$, plus $1$ more is $15$.
  • Try Making a Ten: $8 + 2 = 10$, and $5$ left over makes $15$.

• $9 + 6 = ?$

  • Try Making a Ten: $9$ needs just $1$ to become a $10$. Take $1$ from the $6$ (leaving $5$). $10 + 5 = 15$.