Rules for rounding

Example
A stick of rock is 27 cm long. How long is it to the nearest 10 cm?

Answer
27 cm is between 20 cm and 30 cm. So 27 cm will get rounded to either 20 cm or 30 cm. To get the right answer we need to decide whether 27 is nearer to 20 or 30.

You can see from the picture that it is closer to 30.
So 27 cm is rounded up to 30 cm.
So the stick of rock is 30 cm long when we measure to the nearest 10 cm.

For the same reasons 26, 27, 28 and 29 all get rounded up to 30.
And 21, 22, 23 and 24 all get rounded down to 20

What about 25? It's exactly half way between 20 and 30. It has to be rounded one way or the other.
The rule that everyone usually follows is that 25 gets rounded up to 30.

The Rules
In this way we get the rules about rounding up and down.

1, 2, 3 and 4 get rounded down
5, 6, 7, 8 and 9 get rounded up

These rules work for all numbers, whether you are using tens, hundreds or thousands (or anything else). There is more about these rules in the other factsheets.