A common part of a lot of maths exam questions involves giving your answer to a given number of decimal places. These are easy marks to pick up and do not take long to work out, which means it is a very usefull and important skill to have.

When a question asks for an answer to a given number of decimal places, for example 1 decimal place, the answer should look like this:

20.5 , 16.0, 1.3 etc.

The trick is to be able to round up or down when the answer to a question comes out on a calculator with lots of decimal numbers eg. 2.5678239 . . .

The golden number in terms or rounding up or down is 5. When rounding, say, a two digit decimal number to a 1 decimal place, If the second decimal place is below 5 then the 1st decimal digit stays as it is. If the second decimal is 5 or above then the 1st decimal digit increases by one.

Example 1.

Required answer needs to be to one decimal place, but the answer has come out on the calculator as : 4 . 169

The 1st decimal number is 1, the 2nd is 6, and as this is higher than 5 it means that the 1st decimal place gets increased by on, leaving the answer at 4.2

Some more examples:

34 . 782 becomes 34 . 8

100.254 becomes 100.3

2 . 927 becomes 2.9

When the answer is required to be to 2 decimal places the same steps are used, but the 3rd decimal digit is assessed in order to adjust the 2nd.
For example
34 . 782 becomes 34.78

100 . 254 becomes 100 . 25

2 . 927 becomes 2.93

These steps can be applied to all numbers and are relatively easy marks in exams. However do bear in mind that if any rounding is done, the answer will be less accurate than the longer version of the answer. This means that if any rounding is done halfway through an equation and the rounded number is used, the final answer will be slightly out.