Rounding

Rounding

Decimal Places

Often you are asked to write an answer to a given number of decimal places (be careful to read the question properly!).

What you need to do:

1. Count the number of decimal places you need.

2. Look at the next digit. If it's 4 or below just write down the answer with the right amount of decimal places. If it's 5 or above write down the number but put your last decimal place up by one.

For example: 2.3635 to two decimal places

For example: 53.586 to two decimal places

What if the last digit is a 9?

A 9 goes up to a 10 so you need to put a zero in the last column and add one to the previous number.

For example: 8.6397 to three decimal places

Try this one! Type in what you think the answer is and click the button to see whether you are right:

Tips!

If you are not told how many places to write just be sensible! Generally, you should go to one more place than the numbers used in the question.

With angles, no more than one decimal place should be used unless told otherwise.

Significant Figures

These involve all digits, not just decimal places. Zeros are only "significant" if they separate two other non-zero digits!

What you need to do:

1. Start counting at the first non-zero digit until you have the number of digits that you need.

2. Look at the next digit. If it's a 4 or below just write the number down leaving the last digit the same. If it's a 5 or above put the last digit up by one.

3. If you are rounding whole numbers (i.e. to the left of the decimal point) put zeros in all the other columns after your last digit until you reach the decimal point.

e.g. 12 736 to three significant figures is 12 700

e.g. 6530 to one significant figure is 7000

e.g. 0.576 to two significant figures is 0.58

Try this one! Type in the answer and click the button to see if you are right:

Tip!

In real situations, use common sense to decide on your accuracy. E.g. Length of a back garden would not be written as 8.5632 metres. It would be more sensible to write 8.6 metres!