Page 33 - MAT KS3 Y8 Cambridge CheckPoint

3 Place value, ordering and rounding

We use numbers every day, but we do not always need them to be Key words
exact. Numbers are often rounded. This is because it is easier to
work with rounded numbers and compare them. Make sure you learn and
understand these key words:
You can usually round numbers when exact accuracy isn’t
powers of 10
important. For example, look at these two newspaper articles.
power
Real Madrid take Real Madrid take index
the top spot! the top spot! round
degree of accuracy
On Saturday afternoon 74 836 On Saturday afternoon 75 000
equivalent calculation
football fans saw Real Madrid football fans saw Real Madrid
approximate
beat FC Barcelona by 2 goals beat FC Barcelona by 2 goals
to take the top spot in La Liga to take the top spot in La Liga
(Spain’s top football league). (Spain’s top football league).

The first article gives the accurate number of football fans, 74 836. The second article rounds the
number to 75 000. This means the second article is easier to read, and it really isn’t important to
the story whether 74 836 or 75 000 football fans were there to watch the game.
For market research, companies usually use accurate numbers in their calculations. They will
generally round their answers to give final figures that are easier to compare.
For example, a mobile phone company may look at the population figures of different countries and
the numbers of mobile phones used in those countries. They may use these figures to help them decide
how to increase sales of mobile phones or to decide whether more network coverage is needed.
Look at this information about Bangladesh and Hong Kong.

Bangladesh Hong Kong
Population: 158 570 535 Population: 7 122 508
Number of mobile phones: 74 192 350 Number of mobile phones: 13 264 896
Number of mobile phones per person: 0.467 882... Number of mobile phones per person: 1.862 391...

Even though Bangladesh has a much bigger population than Hong Kong,
when you compare the number of mobile phones per person, you can
see that there are more mobile phones per person in Hong Kong than
Bangladesh.
You can round both the decimal numbers that have been calculated and
say that there are approximately 0.5 mobile phones per person
in Bangladesh compared with about 2 mobile phones per person in
Hong Kong.

In this unit you will learn more about rounding. You will also learn about calculating with decimal
numbers, as well as estimating and approximating.

3 Place value, ordering and rounding 31