Rounding Whole Numbers to the Nearest 10 or 100

Section 1

Why Do We Round Numbers?

Have you ever been at a store and heard someone say, "That costs about five dollars"? They didn't give the exact price — they rounded it! People have been rounding numbers for thousands of years because sometimes you don't need an exact number. A close, simpler number works just fine.

Rounding makes numbers easier to think about. Imagine trying to add 347 + 682 in your head. That's hard! But if you round them to 350 + 680, it's much easier. People who build houses, cook food, and even launch rockets use rounding every single day.

Long, Long Ago

Ancient farmers counted their sheep in groups of ten. If they had 38 sheep, they'd say "about 40." This was one of the first kinds of rounding!

Hundreds of Years Ago

Shopkeepers began rounding prices to make giving change faster. "That's about 2 gold coins" was easier than counting tiny coins.

In Schools Today

You learn rounding in 3rd grade because it helps you estimate — which means making a smart guess. Estimating helps you check if your answers make sense.

In the Real World

Scientists, builders, and cooks all round numbers. A weather reporter says "about 70 degrees" instead of "68.4 degrees" because it's easier to understand quickly.

So, the big question is: How do we round a number the right way? That's exactly what you'll learn in this lesson!

Section 2

Core Ideas You Need to Know

Before we start rounding, let's review a few important ideas. These are the building blocks that make rounding work.

Place Value

Every digit in a number has a special spot, or place. In the number 463, the 4 is in the hundreds place, the 6 is in the tens place, and the 3 is in the ones place.

Rounding Means Finding the Closest "Friendly" Number

When you round to the nearest 10, you find which number ending in 0 is closest. When you round to the nearest 100, you find which number ending in 00 is closest.

The Digit to the Right Decides

Look at the digit just to the right of the place you're rounding to. If it's 0, 1, 2, 3, or 4, round down. If it's 5, 6, 7, 8, or 9, round up.

The Number Line Is Your Best Friend

A number line helps you see which "friendly" number is closer. We'll use one in the next section!

✦ Key Takeaway

Think of rounding like standing between two houses on a street. You want to walk to the closer house. If you're right in the middle (the digit is 5), you always walk to the bigger house (round up). That's the rule!

Section 3

See It on a Number Line

Let's round the number 37 to the nearest ten. First, think: what are the two tens that 37 sits between? That's 30 and 40. Now look at where 37 is on the number line below.

Since 37 is past the halfway point (35), it is closer to 40 than to 30. So we round 37 up to 40. The ones digit is 7, which is 5 or more — so we round up!

Now let's try 32. The ones digit is 2. That's less than 5, so 32 is closer to 30. We round 32 down to 30.

Section 4

How to Round to the Nearest 10

Here are the steps you follow every time you round a number to the nearest ten. Let's use the number 63 as our example.

The Rounding Rule

Look at the ones digit

If the ones digit is 0, 1, 2, 3, or 4 → round down | If it is 5, 6, 7, 8, or 9 → round up

Rounding 63 to the Nearest 10

Step 1 — Find the tens that surround your number63 is between 60 and 70.

Step 2 — Look at the ones digitIn 63, the ones digit is 3.

Step 3 — Decide: round up or down?3 is less than 5, so we round down.

Step 4 — Write your answer63 rounded to the nearest ten is 60.

What if the ones digit is exactly 5? For example, the number 45. The digit 5 is the halfway point. The rule says: when the digit is 5, always round up. So 45 rounds to 50.

✦ Key Takeaway

Imagine you're climbing a hill. Numbers 1, 2, 3, and 4 slide back down to the bottom. But 5, 6, 7, 8, and 9 have enough push to go over the top! That's how you remember: 5 or more rounds up.

Section 5

Rounding to the Nearest 100

Rounding to the nearest 100 works the same way, but now you look at the tens digit instead of the ones digit. Let's try rounding 368 to the nearest hundred.

Here's how we did it:

Rounding 368 to the Nearest 100

Step 1 — Find the hundreds around your number368 is between 300 and 400.

Step 2 — Look at the tens digitIn 368, the tens digit is 6.

Step 3 — Decide: round up or down?6 is 5 or more, so we round up.

Step 4 — Write your answer368 rounded to the nearest hundred is 400.

Number	Tens Digit	Round Up or Down?	Rounded to Nearest 100
123	2	Down (2 < 5)	100
450	5	Up (5 = 5)	500
781	8	Up (8 > 5)	800
649	4	Down (4 < 5)	600
550	5	Up (5 = 5)	600

Section 6

Worked Example — Step by Step

Let's solve one complete problem together. We'll round the number 274 two ways: first to the nearest ten, and then to the nearest hundred.

Part A: Round 274 to the nearest 10

Step 1 — Find the two tens around 274274 sits between 270 and 280.

Step 2 — Look at the ones digitThe ones digit in 274 is 4.

Step 3 — Decide4 is less than 5, so we round down.

Step 4 — Answer274 rounded to the nearest ten = 270

Part B: Round 274 to the nearest 100

Step 1 — Find the two hundreds around 274274 sits between 200 and 300.

Step 2 — Look at the tens digitThe tens digit in 274 is 7.

Step 3 — Decide7 is 5 or more, so we round up.

Step 4 — Answer274 rounded to the nearest hundred = 300

Did you notice? The same number can round to different values depending on whether you're rounding to the nearest ten or the nearest hundred. That's totally normal!

Section 7

Rounding to 10 vs. Rounding to 100

When should you round to the nearest 10, and when should you round to the nearest 100? It depends on how exact you need to be! Let's compare.

	Round to Nearest 10	Round to Nearest 100
Which digit do you look at?	The ones digit	The tens digit
Your answer ends in…	0 (like 30, 70, 150)	00 (like 200, 500, 800)
How close is it?	Very close — no more than 5 away	Less close — could be up to 50 away
Best for…	Quick math, estimating small amounts	Big-picture thinking, large amounts
Example: 847	850	800

Rounding to the nearest 10 gives a closer answer. Rounding to the nearest 100 gives a simpler answer. Both are useful!

✦ Key Takeaway

Rounding to 10 is like zooming into a map — you see more detail. Rounding to 100 is like zooming out — you see the bigger picture. Both views help you understand the world!

Section 8

What Comes Next?

Now that you know how to round to the nearest 10 and 100, guess what? You can use the same exact steps to round even bigger numbers! In 4th grade, you'll round to the nearest 1,000 and even 10,000.

Rounding To…	Look At…	Example: 4,738
Nearest 10	Ones digit (8)	4,740
Nearest 100	Tens digit (3)	4,700
Nearest 1,000	Hundreds digit (7)	5,000

You'll also learn to estimate answers to addition and subtraction problems by rounding first. For example, to estimate 389 + 214, you could round to 400 + 200 = 600. That's a super-fast way to check your work!

The rounding skills you're learning right now are the foundation for all of that. You're building something important!

Section 9

Practice Problems

Try these problems on your own! Click "Show Answer" when you're ready to check your work.

PROBLEM 1 — THINKING QUESTION

When you round a number to the nearest 10 and the ones digit is 3, do you round up or down? Why?

PROBLEM 2 — ROUND TO THE NEAREST 10

Round 86 to the nearest ten.

PROBLEM 3 — ROUND TO THE NEAREST 100

Round 541 to the nearest hundred.

PROBLEM 4 — REAL-WORLD PROBLEM

Your school collected 378 cans of food. The principal wants to tell everyone "about how many" cans were collected. Round 378 to the nearest ten and to the nearest hundred.

PROBLEM 5 — CHALLENGE!

I'm thinking of a number. When I round it to the nearest ten, I get 250. What is the smallest number I could be thinking of? What is the largest?

Summary

What You Learned

Rounding means replacing a number with a simpler, nearby "friendly" number. To round to the nearest 10, look at the ones digit. To round to the nearest 100, look at the tens digit. If the digit you look at is 0, 1, 2, 3, or 4, round down. If it is 5, 6, 7, 8, or 9, round up.

A number line helps you see which friendly number is closer. Rounding to 10 gives a close estimate, while rounding to 100 gives a bigger-picture estimate. Both are helpful for estimating, checking your work, and making numbers easier to use in everyday life. You can use these same steps to round to 1,000 and beyond as you grow as a mathematician!