Topics
1. Number and place value
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Australia
Year 5

1.04 Round numbers

Lesson
Practice

Are you ready?

Before we look at rounding to different place values, check if you remember how to round to the nearest 10.

Examples

Example 1

Round the number on the number line to the nearest 10.

0102030
Worked Solution
Create a strategy

Look for the closest 10 on the number line.

Apply the idea

The point is closer to 20 than it is to 10.

The rounded value is 20.

Idea summary

  • If you are rounding a number to the nearest 10, think about whether it is closer to the ten above, or the ten below.

  • If a number is exactly in the middle, round to the higher ten.

Round numbers in different ways

In this video we round 362 to the nearest ten, and then round it to the nearest hundred. See how our answer changes, depending on the places we are rounding to.

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Examples

Example 2

Answer the following:

a

Round 7428 to the nearest hundred.

Worked Solution
Create a strategy

Plot the given number on a number line that starts from its hundreds value and ends at the next hundreds value.

Apply the idea

7428 is between 7400 and 7500. So we should use those numbers as end values of the number line.

74007410742074307440745074607470748074907500

We can see from the number line that 7428 is closer to 7400 than 7500.

So, rounding 7428 to the nearest hundred is 7400.

b

Round 7428 to the nearest thousand.

Worked Solution
Create a strategy

Plot the given number on a number line that starts from its thousands value and ends at the next thousands value.

Apply the idea

7428 is between 7000 and 8000. So we should use those numbers as end values of the number line.

70007100720073007400750076007700780079008000

We can see from the number line that 7428 is closer to 7000 than 8000.

So, rounding 7428 to the nearest thousand is 7000.

Idea summary

  • If you are rounding a number to the nearest 100 and 1000, think about whether it is closer to the one above, or the one below.

  • If a number is exactly in the middle, round to the higher number.

Round larger numbers

In the second video, we look at how to round 5 digit numbers, using the rounding rule. We also round a number that has a 9 in one of the places we need to round up. How do we tackle this? Let's find out here:

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Examples

Example 3

Round 974\,321 to the nearest ten thousand.

Worked Solution
Create a strategy

Use a place value table and check the thousands column.

If it is less than 5, we round down. If it's greater than or equal to 5, we round up.

Apply the idea

Put the number in a place value table:

Hundred thousandsTen thousandsThousandsHundredsTensOnes
974321

We can see from the table that the thousands is 4 which is less than 5.

So, we need to round down to the nearest ten thousand. So the ten thousands column should stay the same, and all lower place values should be 0.

Hundred thousandsTen thousandsThousandsHundredsTensOnes
970000

974\,321 rounded to the nearest ten thousand is 970\,000.

Idea summary

Rounding to the nearest place always follows the same rule. No matter how many digits our number has, we always need to think about the place we are rounding our number to. If we round 2678 to the nearest hundred, we get 2700, but if we round it to the nearest thousand we get 3000.

Outcomes

AC9M5N08

check and explain the reasonableness of solutions to problems including financial contexts using estimation strategies appropriate to the context

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