Adding Three Whole Numbers Together

When we add three whole numbers, we combine all three groups to find one total.

Reading is good — doing is better. Practice Adding Three Whole Numbers Together as an interactive lesson.

Definition

Adding three whole numbers means putting three separate amounts together to get one big total. You do it in two steps: first add any two of the numbers, then add the third number to that answer.

Remember the rule

Add two numbers first, then add the third: (A + B) + C = total. The order does not change the answer!

Key words

whole number: A counting number like 0, 1, 2, 3 — no fractions or decimals.
add: To put amounts together to make a bigger amount.
sum: The answer you get after adding numbers together.
equation: A math sentence with numbers and an equals sign, like 2 + 3 + 4 = 9.
plus sign (+): The symbol that tells you to add two amounts together.
equals sign (=): The symbol that means 'is the same as' — what comes before equals what comes after.
group: A set of objects counted together, like 4 apples or 5 blocks.

Worked examples

2 + 3 + 4 = ?

→ 9 · First do 2 + 3 = 5, then do 5 + 4 = 9.

1 + 5 + 2 = ?

→ 8 · First do 1 + 5 = 6, then do 6 + 2 = 8.

Tom has 3 red balloons, 4 blue balloons, and 2 yellow balloons. How many balloons does he have in all?

→ 9 balloons · 3 + 4 = 7, then 7 + 2 = 9.

4 + 4 + 4 = ?

→ 12 · 4 + 4 = 8, then 8 + 4 = 12. All three numbers are the same!

6 + 0 + 3 = ?

→ 9 · Adding zero doesn't change anything: 6 + 0 = 6, then 6 + 3 = 9.

5 + 2 + 8 = ?

→ 15 · Try adding 2 + 8 = 10 first because 10 is easy, then 5 + 10 = 15.

Common mistakes

Forgetting to add the third number and stopping after the first addition step.
Adding only two of the three numbers and leaving one out entirely.
Losing track of which numbers have already been added — use your finger to point to each number.
Thinking the order matters — 1 + 2 + 3 gives the same answer as 3 + 2 + 1, which is 6 either way.
Rushing and making a small adding mistake on the first step, which makes the final answer wrong too.

FAQs

Does it matter which two numbers I add first?

No! You will always get the same total no matter which two you add first. Pick the pair that feels easiest for you.

Can I use my fingers to add three numbers?

Yes! Hold up fingers for the first number, count on more fingers for the second, then keep counting on for the third.

What if one of the numbers is zero?

Zero means nothing is added, so just add the other two numbers together and that is your answer.

How is adding three numbers different from adding two numbers?

It is the same idea — you are just combining one more group. You do two addition steps instead of one.

Can I draw pictures to help?

Absolutely. Draw dots or circles for each number, then count all of them together to find the total.

What if I get confused in the middle?

Write down the answer from your first addition step so you do not forget it, then add the third number to that written answer.

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