Quick Addition and Subtraction Within 20

Being able to quickly add and subtract numbers up to 20 is a superpower in math! Instead of counting on your fingers one by one, you can use smart strategies to find the answer fast.

Strategy 1: Make a Ten

The number 10 is your best friend in math. When adding two numbers, try to make a 10 first.

Let's look at $8 + 9 = ?$

1. Start with the bigger number, $9$. How many more does $9$ need to become $10$? It needs $1$.
2. Take $1$ away from the $8$. Now you have $10$ and $7$.
3. $10 + 7 = 17$

So, $8 + 9 = 17$.

Strategy 2: Use Doubles

Knowing your doubles (like $5+5$, $6+6$, $7+7$) makes addition much easier. You can use them to solve "doubles plus one" or "doubles minus one" problems.

For example, what is $7 + 8$?

1. You know that $7 + 7 = 14$.
2. Since $8$ is just one more than $7$, add $1$ to your answer.
3. $14 + 1 = 15$.

So, $7 + 8 = 15$.

Strategy 3: Subtract by Making a Ten

You can use the "Make a Ten" trick backwards for subtraction!

Let's solve $14 - 6 = ?$

1. First, take away enough to get to $10$. To get from $14$ down to $10$, you subtract $4$. $(14 - 4 = 10)$
2. But you need to subtract $6$ in total. Since you already subtracted $4$, you still need to subtract $2$. $(6 - 4 = 2)$
3. Now, subtract that $2$ from $10$: $10 - 2 = 8$.

So, $14 - 6 = 8$.

Strategy 4: Think Addition to Subtract

Addition and subtraction are opposites. If you are stuck on a subtraction problem, turn it into an addition mystery!

Let's solve $17 - 8 = ?$

1. Ask yourself: "What number plus $8$ equals $17$?"
2. You might remember from your addition facts that $8 + 9 = 17$.
3. Because $8$ and $9$ make $17$, taking $8$ away from $17$ leaves $9$.

So, $17 - 8 = 9$.

Keep Practicing!

The best way to get fast at addition and subtraction within 20 is to practice these strategies. Soon, you won't even need to think about the steps—you will just know the answers from memory!