Subtraction Facts Within 20

When you are subtracting from numbers between 11 and 20, it can seem tricky at first. But with a few simple tricks, you can solve problems like $15 - 8$ in no time!

Here are two helpful strategies to make subtraction easy.

Strategy 1: Make a Ten

One of the best ways to subtract is to get to the number $10$ first. You do this by breaking apart the number you are taking away.

Let's look at $15 - 8$:

1. First, take away enough to make $10$. To turn $15$ into $10$, you need to take away $5$.
2. Since you need to take away $8$ in total, and you already took away $5$, you still have $3$ left to take away (because $8 = 5 + 3$).
3. Now, subtract that $3$ from $10$: $10 - 3 = 7$

So, $15 - 8 = 7$.

Strategy 2: Use an Addition Fact

Addition and subtraction are best friends! If you know your addition facts, you can easily figure out your subtraction facts.

Let's try $13 - 7$:

1. Ask yourself: "What number can I add to $7$ to make $13$?"
2. Write it as a missing number problem: $7 + ? = 13$.
3. If you know that $7 + 6 = 13$, then you know the subtraction answer!

$13 - 7 = 6$

Let's Practice!

Try solving $17 - 9$ using either strategy.

Using Make a Ten:

• Take away $7$ to make a ten: $17 - 7 = 10$.
• You need to take away $9$ total, which is $2$ more.
• $10 - 2 = 8$.

Using an Addition Fact:

• Think: $9 + ? = 17$.
• Since $9 + 8 = 17$, the answer is $8$.

Both ways give you the exact same answer: $17 - 9 = 8$