Addition & Subtraction of Single Digits

Before tackling bigger numbers, let’s make sure single-digit addition and subtraction feel automatic. This is the foundation everything else builds on.

Addition means combining two groups into one. The + sign tells you to combine.

$$3 + 5 = 8$$

Think of it as: you have 3 things, someone gives you 5 more, now you have 8.

Here are the key ideas:

• Order doesn’t matter: $3 + 5 = 5 + 3 = 8$ (this is called the commutative property)
• Adding zero changes nothing: $7 + 0 = 7$
• Adding 1 just means the next number: $6 + 1 = 7$

Doubles are worth memorizing because they come up a lot:

• $1 + 1 = 2$
• $2 + 2 = 4$
• $3 + 3 = 6$
• $4 + 4 = 8$
• $5 + 5 = 10$

Once you know doubles, “doubles plus one” is easy:

• $3 + 4 = 3 + 3 + 1 = 7$
• $5 + 6 = 5 + 5 + 1 = 11$

Pairs that add to 10 are super useful later on:

• $1 + 9 = 10$
• $2 + 8 = 10$
• $3 + 7 = 10$
• $4 + 6 = 10$
• $5 + 5 = 10$

Subtraction means removing one amount from another. The $-$ sign tells you to take away.

$$9 - 4 = 5$$

You had 9 things, took away 4, and 5 are left.

Key ideas:

• Subtracting zero changes nothing: $8 - 0 = 8$
• A number minus itself is zero: $6 - 6 = 0$
• Order matters: $9 - 4 = 5$ but $4 - 9$ gives a negative number (we’ll cover that later)

Instead of “take away,” you can think: what do I add to get there?

$8 - 3 = ?$ is the same as asking $3 + ? = 8$. The answer is 5.

This “missing addend” way of thinking is really helpful when the subtraction feels tricky.

$7 + 6$

Think: $7 + 3 = 10$, then $10 + 3 = 13$. So $7 + 6 = 13$.

Or use doubles: $6 + 6 = 12$, plus 1 more = 13.

$9 - 7$

Think: $7 + ? = 9$. The answer is 2. So $9 - 7 = 2$.

$8 + 5$

Think: $8 + 2 = 10$, then $10 + 3 = 13$. So $8 + 5 = 13$.