NUMBER

Rounding and Estimating

Rounding and Estimating

GCSE Maths revision : Numbers

To help make an answer easier to understand it can help to round it up or down, or to estimate what the answer will be. If you’re asked in a question to give an answer in its simplest form then this will be what you’re expected to do.

Large numbers can be rounded up or down, for example the number of people at a festival or attending a university.

For example: round 35680 to the nearest thousand.

The thousands digit is 5. This means that the nearest thousand must lie between 5000 and 6000.

The next digit in the hundreds is 6. Therefore, you have to round up to 6000 because 600 is closer to 6000 then 5000.

So, the answer is: 36000.

What about rounding to the nearest hundred?

So, we know that the digit in the hundreds is 6. the following number in the tens is 8. 80 is closer to 700 than 600 so the answer is 35700.

You may also need to round up or down decimals. Sometimes an answer can come up with lots of decimal places. So, numbers can be rounded up to a certain number of decimal places.

For example: round 4.5793 to 2 dp (2 decimal places).

For two decimal places you need to look at the number in third decimal place. Is it above or below 5? If it’s 5 or above you need to round the next number up. If it’s below then the next number stays the same.

In this example the number in third decimal place is 9 so we need to round the 7 up to 8.

So, the answer is: 4.58 (2 dp).

The following example is slightly different: round 3.598 to 2 dp.

As 8 is larger than 5 you need to round the 9 up. However, this would round it up to 10 so the following number is also rounded up one.

So, the answer is: 3.60.

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Estimating

GCSE Maths revision : NumbersIf there’s no need to get an exact answer then estimating is a good way to get a rough idea.

For this you simply need to round up or down the figures to make them easier to work with.

For example: what’s an approximate answer to 58838 x 0.0456?

First of all, round up or down both sides:

60000 x 0.05

And now you can work out an approximate answer: 3000

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