## Try This - Rounding

Presenting information : Values are often rounded, and using these rounded numbers in calculations can give answers like 809.2 people. Here we can round the answer down to 809 people, because we know it must be a whole number and it is more likely to be 809 than 810.

When we want to give a number as a whole number, a decimal that is greater than 0.5 is rounded up, and a decimal that is less than 0.5 is rounded down. A decimal that is exactly 0.5 is usually rounded up. We can use the 809.2 people as an example to show how this is done. Because we are rounding to a whole number, we need to look at the decimal part, which is .2. This is less than 0.5, so we round down, giving us 809 people. However, if the number of people had been 809.7, we would round up to give 810.

Rounding is not only used to make whole numbers. Often rounding is used to make long decimal numbers shorter. For example, we could round 63.87 up to 63.9.

In fact, a figure like 85% must itself have been rounded to give a whole-number percentage. This means that it could originally have been any percentage greater than 84.5% and less than 85.5%. The precise result of expressing 809 people as a percentage of 952 is a long number beginning 84.9789, and going on for many more decimal places. It makes sense to round this percentage up to 85% in this context. (But if greater precision were required, rounding to 85% might be unacceptable.) If we use the same method of calculation as before we can work out that this 85% could represent any number of people between 804 and 813.

To find out how to read a chart go to Try this: Reading a chart