Grade 3 (age 8-9)

grade 3 Rounding Numbers

Estimating means using a nearby round number, such as a ten or a hundred, instead of the exact value to say about how much something is. You do it all the time, for example when you guess roughly how much your shopping will cost before you pay. You can round to the nearest ten, always round up or always round down; to round to the nearest ten, a ones digit of 0 to 4 goes down and 5 to 9 goes up. Change the number to see which ten it is closer to on the number line, and compare the three results side by side on the bars.

What Is Estimating?

🎯 Making a Good Guess

①Using a nearby ten or hundred instead of the exact value is called estimating

②It helps whenever a rough size is more useful than an exact answer, like guessing the cost of your shopping

③There are three ways: round to the nearest ten, always round up, or always round down

Rounding on a Number Line

Number37

💡 Rounding Goes to the Closer Ten

①On the number line, 37 is closer to 40 than to 30, so 37 rounds to 40

②A ones digit of 0, 1, 2, 3 or 4 goes down to the lower ten, and 5, 6, 7, 8 or 9 goes up to the higher ten

③A number right in the middle, like 35, is rounded up by agreement

④Rounding up and rounding down always go one way, no matter which ten is closer

Comparing Three Ways

📊 Which Way When?

①Round up when you must not fall short: 32 people riding in 10-seat vans need 4 vans

②Round down when leftovers do not count: 37 candies packed 10 to a bag fill only 3 bags

③Round to the nearest ten when you only need a rough size, like about how many people are in the playground

Summary

Nearest Ten

Ones digit 5 or more: up; less than 5: down

Look at the ones digit to round to the tens

Round Up

31 → 40, 37 → 40

If the ones digit is not 0, always go up to the next ten

Round Down

31 → 30, 37 → 30

Change the ones digit to 0 and go down to the ten below

🎯 Summary

①To round to the nearest ten, a ones digit of 5 or more goes up and less than 5 goes down

②Rounding up gives the same or a bigger number, and rounding down gives the same or a smaller one

③Round up when you must not fall short, round down when leftovers do not count, and round to the nearest ten for a rough size

④Rounding to the nearest ten means moving to the closer ten on the number line

⑤Say an estimate with about, as in about 40

Examples and Unit Test

Example 1

Round 37 to the nearest ten.

Look at the ones digit. The ones digit of 37 is 7.

7 is 5 or more, so round up to 40.

▸ 40

On the number line, 37 is closer to 40 than to 30.

Example 2

Round 42 to the nearest ten.

The ones digit of 42 is 2.

2 is less than 5, so round down to 40.

▸ 40

37 and 42 both round to 40, but 37 goes up and 42 goes down.

Unit Test

Round 53 up to the tens.

①50

②53

③60

④40

▸ ③ 60

Rounding up always moves to the next ten if the ones digit is not 0.

The ones digit of 53 is 3, not 0, so it becomes 60.

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Introduction to Fractions

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Last updated 2026-10-17