Why Do We Add Three Numbers?
People have been adding things together for a very, very long time! Long ago, even before there were schools, kids and grown-ups needed to count things they had. Imagine you pick some apples from three different trees. You want to know how many apples you have in all. That is why we learn to add!
Adding two numbers is great. But in real life, we often have three groups of things to put together. Maybe you have red crayons, blue crayons, and green crayons. Or maybe you ate some grapes at breakfast, lunch, and dinner. Adding three numbers helps you find the total!
The big question we will answer today is: When a word problem gives us three groups of things, how do we find the total? We will use pictures, objects, and number sentences to figure it out!
Big Ideas About Adding Three Numbers
Before we start solving word problems, let's learn four big ideas. These ideas are like superpowers that help you add three numbers!
Read the Story
Draw a Picture
Write a Number Sentence
Add in Any Order
See It With Pictures!
Let's look at a word problem and draw a picture to solve it. Here is the problem:
We can draw circles or use real pictures to show each group. Look at the picture below!
We drew 4 red circles, 5 blue circles, and 3 yellow circles. Then we counted all of them: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12! Mia has 12 balloons in all. Drawing a picture is a great way to see the answer!
How to Write a Number Sentence
A number sentence is a math sentence that uses numbers and symbols. When we add three numbers, our number sentence has two plus signs and one equals sign.
Here is a trick to make adding easier! Look for two numbers that make 10. Adding to 10 is easy because you already know those facts. Then just add the last number to 10.
You can also add the first two numbers and then add the third number to that answer. Both ways give you the same sum!
No matter which way you add, the answer stays the same. You can pick the way that feels easiest to you!
Different Ways to Solve
There are many ways to add three numbers. Let's look at all the tools you can use!
| Way to Solve | What You Do | When It Helps |
|---|---|---|
| Use Objects | Draw pictures or use real things. Count them all. | When you want to see each thing. |
| Number Line | Start at 0 and hop forward by each number. | When numbers are small and easy to hop. |
| Make a 10 | Find two numbers that add up to 10 first. | When two of the numbers make 10. |
| Add Step by Step | Add the first two, then add the third. | Works every time! |
All four ways give you the same answer. Pick the one that feels best to you!
Let's Solve One Together!
Helpful Tips and Common Mistakes
| ✅ Do This | ❌ Watch Out For This |
|---|---|
| Read the whole problem before you start adding. | Starting to add before you find all three numbers. |
| Draw a picture or use objects to help you count. | Trying to do it all in your head when you're not sure. |
| Look for pairs that make 10. | Forgetting to add the third number. |
| Check that your answer is 20 or less. | Counting too fast and missing a number. |
| Count your drawing carefully, pointing to each one. | Counting the same object twice. |
What Comes Next?
You are doing an amazing job learning to add three numbers! Here is what you will learn as you keep growing as a math star.
| What You Know Now | What's Coming Next |
|---|---|
| Adding three numbers up to 20 | Adding bigger numbers — even up to 100 and more! |
| Using pictures and objects | Using just numbers in your head (mental math!) |
| Finding the total (sum) | Solving problems with adding and subtracting together |
| Adding three numbers | Adding four, five, or even more numbers |
Every big math idea starts with the small steps you are taking right now. Adding three numbers is a building block for everything that comes next. Keep practicing and you will be ready!
Practice Problems
Try these five problems. Use pictures, fingers, or objects to help. When you are ready, click Show Answer to check your work!
What We Learned
Today we learned how to solve word problems that ask us to add three whole numbers with a sum of 20 or less. We practiced finding the numbers hiding in a story and writing a number sentence with two plus signs and an equals sign. We used pictures and objects to see each group, then counted them all to find the total.
We also learned a super helpful trick: look for two numbers that make 10, then add the third number. We can add numbers in any order and still get the same answer. Whether you draw pictures, use a number line, or find a pair that makes 10, the most important thing is to read carefully, find all three numbers, and add them together. Keep practicing and you will get faster and faster! 🎉