Åk 6–9
5.3 Rules for Rounding
When you round off natural numbers, you round them off to the nearest tens, hundreds, thousands and so forth.  We can see this is the number line with a few examples:

If we need to round off the number 17 to the nearest ten and put this on the number line, we can see that the number 17 is closer to 20 than 10.  So we round up the number 17 to 20.

We can take another example:

Round off  the number 320 to the nearest hundred.  We can see that it is close to 300 then 400.  So the number 320 is rounded down to 300.

The last example is a little tougher:

Round off the number 55 to the nearest ten.  Here we see that it is equally long between 50 and 55 as it is between 55 and 60.  Normally we round up, in other words to 60.

Here are a few examples:

1. Round off the number 346 to the nearest tens.
We look at the number after the 4 and see that it is a 6.  Then we round up the number to 350.

2. Round off 855 to the nearest hundreds.

Here we look at the tens digit after the 8 and see that is a 5.  We then round the number up to 900.

3. Round off the number 243,579 to the ten thousands.

Here we look at the digit after the ten thousands place and see that it is a 3.  The number is therefore rounded down to 240,000.