Rounding Numbers

What Is Rounding?

Sometimes we do not need an exact number. We just need one that is close and easier to use. Rounding is the way we make a number simpler by moving it to a nearby round number.

A "round" number is one that ends in zero, like 10, 20, 30, or 100, 200, 300. These numbers are friendly because they are easy to add, compare, and say out loud.

For example, if 28 children come to a party, you might say "about 30 children came." That is rounding! 28 is close to 30, so 30 is a good simple answer.

Why Do We Round?

Rounding is a real-life superpower. Here are some reasons we use it:

• To estimate. If a toy costs 19 pounds and another costs 31 pounds, you can round to 20 and 30 and quickly know it is "about 50 pounds" for both.
• To check answers. If you add 41 + 38 and get 79, you can round to 40 + 40 = 80. Since 79 is close to 80, your answer looks sensible.
• To make big numbers easy. Saying "about 600 people" is easier than "597 people."

Rounding to the Nearest 10

Let's start by rounding to the nearest 10. The round numbers we can choose are 10, 20, 30, 40, and so on.

The key step: look at the ones digit (the last digit). It tells you which way to go.

The 5-or-more rule: If the ones digit is 5 or more, round up. If it is 4 or less, round down.

Think of a number line. Every number sits between two round tens. We pick the one it is closest to.

Worked example 1. Round 47 to the nearest 10.

47 sits between 40 and 50. The ones digit is 7. Since 7 is 5 or more, we round up to 50.

Worked example 2. Round 23 to the nearest 10.

23 sits between 20 and 30. The ones digit is 3. Since 3 is 4 or less, we round down to 20.

Worked example 3. Round 65 to the nearest 10.

The ones digit is exactly 5. The rule says 5 rounds up, so 65 becomes 70.

Here is a handy chart:

Number	Ones digit	5 or more?	Rounds to
12	2	No	10
47	7	Yes	50
65	5	Yes	70
84	4	No	80

Why 5 Rounds Up

You might wonder: 5 is right in the middle between 0 and 10, so why round up? Mathematicians made a simple, fair rule so everyone does the same thing: 5 always rounds up. This way, there is never any confusion. As long as we all follow the same rule, our rounded numbers match.

Rounding to the Nearest 100

Rounding to the nearest 100 works the same way, but now we look at a different digit. The round numbers are 100, 200, 300, and so on.

The key step: look at the tens digit this time. Apply the same 5-or-more rule.

Worked example 4. Round 380 to the nearest 100.

380 sits between 300 and 400. The tens digit is 8. Since 8 is 5 or more, we round up to 400.

Worked example 5. Round 612 to the nearest 100.

612 sits between 600 and 700. The tens digit is 1. Since 1 is 4 or less, we round down to 600.

To round well, it really helps to understand which digit means what. If you want to brush up, read place value: tens and ones.

A Number Line Helps

If you ever feel stuck, draw a number line. Mark the two round numbers on each end and put your number in between. Then ask: which end is it closer to?

For 47 on a line from 40 to 50, the 7 means it is past the halfway mark (45), so it leans toward 50. That matches our rule!

Rounding and Estimating

Once you can round, you can estimate sums fast. This connects to your addition and subtraction skills.

Worked example 6. Estimate 58 + 41.

Round 58 to 60 and 41 to 40. Now add the easy numbers:

60 + 40 = 100

So the answer is about 100. (The exact answer is 99, very close!) Estimating like this lets you check your work in seconds.

Try It Yourself

Practise with these:

1. Round to 10. Round these to the nearest 10: 16, 34, 55, 72, 89. (Answers: 20, 30, 60, 70, 90.)
2. Round to 100. Round these to the nearest 100: 240, 350, 690, 810. (Answers: 200, 400, 700, 800.)
3. Shopping estimate. Imagine buying things that cost 19p, 32p, and 48p. Round each to the nearest 10, then add. About how much is it altogether?
4. Make your own. Pick any two-digit number. Round it to the nearest 10. Then explain to someone why it rounds up or down.

Now you can round like a pro and make tricky numbers nice and simple. Great work! 🌟