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1.12 Round numbers


Are you ready?

We've seen how to  break up, or partition, numbers  , up to the thousands. Understanding how to do this will help us with our estimating.


Enter a three digit number into the applet and drag the place value cards around to see what amount each digit represents.

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The place value cards can be used to write the expanded form of the numbers.


Example 1

Fill in the boxes with the missing numbers.


Worked Solution
Create a strategy

Write the first number in a place value table.

Apply the idea

Here is the complete table:


We have 6 hundreds which equals 600.

We have 9 tens which equals 90.

We have 8 units which equals 8.

\displaystyle 698\displaystyle =\displaystyle 600+90+8
Idea summary

We can use a place value table to write a number in expanded form.

Round numbers to the nearest 10

Sometimes we may need to solve problems by estimating. We can see if our number is closer to the ten before it, or after it. Let's see how we round our number to the nearest ten.

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Example 2

Round 54 to the nearest ten.

Worked Solution
Create a strategy

Plot 54 on a number line and look for the closest 10.

Apply the idea

Based on the number line, 54 is closest to 50.

The rounded value is 50.

Idea summary

To round a number to the nearest 10, plot the number on a number line to see which ten is closest to the number.

Rounding numbers in more ways

We can also round to the nearest hundred or thousand. Let's see how.

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Example 3

Round 370 to the nearest hundred.

Worked Solution
Create a strategy

Plot 370 on a number line and look for the closest 100.

Apply the idea

Based on the number line, 370 is closest to 400.

The rounded value is 400.

Idea summary
  • If you are rounding a number to the nearest 10, think about whether it is closer to the one above, or the one below. For example, 20 or 30.

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

  • This is the same for hundreds.



applies place value to order, read and represent numbers of up to five digits

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