Why Do We Subtract Tens?
People have been counting in groups of ten for a very, very long time. Can you guess why? Look at your hands — you have 10 fingers! That is why the number 10 is so special.
Long ago, people used pebbles, sticks, and beads to count. They put things into piles of ten so it was easier. When they needed to take some away, they moved whole piles at once. That is exactly what we will learn today!
Today's question is simple: If I have some groups of ten, and I take away some groups of ten, how many do I have left? Let's find out!
Big Ideas to Know
Before we start, let's learn four big ideas. These will help everything make sense.
What Is a Multiple of 10?
What Does Subtract Mean?
Tens Are Like Bundles
The Answer Is 0 or More
See It with Blocks!
Let's look at a picture. We will show 70 − 30 using base-ten blocks. Each long bar is one group of 10.
Look at the picture above. We started with 7 ten-bars (that is 70). We crossed out 3 ten-bars (that is 30). The green bars that are left show us the answer: 4 ten-bars, which is 40!
Here is the secret trick: 7 tens take away 3 tens is 4 tens. You just subtract the tens digit! 7 − 3 = 4, so 70 − 30 = 40. That is it!
How It Works
When you subtract multiples of 10, you can think of it in two easy steps.
See? You are really just doing a small subtraction problem (like 7 − 3) and then putting a zero on the end. Let's try another one: 90 − 50. That is 9 tens minus 5 tens, which equals 4 tens — 40!
What if the two numbers are the same? Like 60 − 60? Well, 6 tens minus 6 tens is 0 tens. The answer is 0. That is okay! Zero means nothing is left.
This number line shows 80 − 50. We start at 80 and jump back by 10 five times. We land on 30. Each hop is one group of ten going away!
Subtraction Chart for Tens
Here is a handy chart. It shows lots of subtraction problems with multiples of 10. See if you can find a pattern!
| Problem | Tens Way | Answer |
|---|---|---|
| 30 − 10 | 3 tens − 1 ten | 20 |
| 50 − 20 | 5 tens − 2 tens | 30 |
| 60 − 40 | 6 tens − 4 tens | 20 |
| 80 − 30 | 8 tens − 3 tens | 50 |
| 90 − 60 | 9 tens − 6 tens | 30 |
| 70 − 70 | 7 tens − 7 tens | 0 |
| 40 − 10 | 4 tens − 1 ten | 30 |
| 90 − 90 | 9 tens − 9 tens | 0 |
Did you see the pattern? Every answer also ends in zero! That is because tens minus tens always gives you tens (or zero). The ones place stays at 0 the whole time.
Let's Solve One Together!
Here is a word problem. Let's solve it step by step.
When Can You Use This?
This skill is super helpful! But it works best in some places. Let's see.
| Works Great! ✅ | Not Quite Yet ❌ |
|---|---|
| Both numbers end in 0 | A number does NOT end in 0 (like 53 − 20) |
| The first number is bigger or the same | The first number is smaller (like 20 − 50) |
| Numbers are between 10 and 90 | Numbers bigger than 90 (you will learn that later!) |
Right now, you are working with numbers from 10 to 90 that all end in zero. Later, you will learn to subtract other numbers, too. But this is the first step — and it is a big one!
What Comes Next?
You are building a very important skill. Here is how it grows as you keep learning.
| What You Know Now | What You Will Learn Soon |
|---|---|
| 70 − 30 = 40 (tens only) | 73 − 30 = 43 (tens and ones mixed) |
| Numbers up to 90 | Numbers up to 100 and beyond |
| Use blocks and number lines | Do it in your head — mental math! |
Every time you solve a problem like 80 − 40, your brain is getting stronger. Soon you will be able to subtract any two-digit numbers. You are doing amazing work!
Practice Time!
Try these five problems. Think about your tens. When you are ready, click the button to see the answer!
What We Learned
Today you learned how to subtract multiples of 10. A multiple of 10 is a number that ends in zero, like 10, 20, 30, 40, 50, 60, 70, 80, and 90. When you subtract one from another, you think about how many groups of ten each number has. Then you subtract those groups — just like a small subtraction problem! For example, 80 − 50 means 8 tens minus 5 tens, which is 3 tens = 30. The answer is always a multiple of 10 (or zero).
You can use base-ten blocks to see it, a number line to hop it, or just think about the tens digit in your head. This skill helps you get ready for even bigger subtraction problems. Keep practicing — you are doing a wonderful job!