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There are many situations where it is not necessary to give an exact number.

For example, if there are \(54785\) people living in a town, you could say that the population is approximately \(55000\).

\(54785\) has been rounded to the nearest thousand to give \(55000\).

Rounding to the nearest 1,000

What is \(1484.5\) rounded to the nearest \(1000\)?

It is between \(1000\) and \(2000\), but it is closer to \(1000\), so round down.
\(1484.5\) rounded to the nearest thousand is \(1000\).

Rounding to the nearest 100

What is \(1484.5\) rounded to the nearest \(100\)?

\(1484.5\) is between \(1400\) and \(1500\), but it is closer to \(1500\), so round up.
\(1484.5\) rounded to the nearest hundred is \(1500\).

Rounding to the nearest 10

What is \(1484.5\) rounded to the nearest \(10\)?

\(1484.5\) lies between \(1480\) and \(1490\), but it is closer to \(1480\), so round down.
\(1484.5\) rounded to the nearest ten is \(1480\).

Rounding to the nearest whole number

What is \(1484.5\) rounded to the nearest whole number?

\(1484.5\) is exactly half way between \(1484\) and \(1485\). We use the rule ‘Round up if a number is exactly half way.’

\(1484.5\) rounded to the nearest whole number is \(1485\).

Estimation is used to find rough answers to calculations.

This can be can be useful in a lot of everyday situations:

• checking if you have enough money to pay for the items in a shop

• estimating how much paint is needed when decorating

• working out how much food to order for a party

Gardeners, caterers, builders, joiners, shopkeepers and engineers are just a few of the people who use estimation on a daily basis.

When estimating rounded numbers are used so that it is quicker and easier to get an approximate answer.

Example

Rory is calculating \({11.87}\times{48}\) using a paper and pencil method.

First he estimates the answer.

\({12}\times{50} = {600}\)

When he finishes his calculation and gets an answer of \(5697.6\), he knows that this cannot be right and that the correct answer is \(569.76\).