In many GCSE Maths exam questions you will be asked to round a number to a specified number of decimal places or significant figures.
To do this simply count the number of decimal places required (in the examples below its 2). Then look at the next digit along. If it’s 4 or less then just write in the number with the correct amount of decimal places. If the last decimal to round is 5 or above, write in the number with the last decimal place up by 1.
For example 1.3721 – becomes 1.37 (as the following 2 is less than 5).
Or 7.48.65 – becomes 7.49 (as the following 6 is greater than 5).
If the last digit is 9 then you need to put a zero in the last column and add 1 to the previous number.
Example 4.698 – becomes 4.70
If the question does not specify how many decimal places to round to just use your own judgement. Currency should be rounded to 2 decimals to denote pounds and pence e.g. £3.69. Angles are rarely rounded to more than 1 decimal place.
Significant figures involve using all the digits specified not just the decimal places.
Begin by counting from the first number greater than zero, until you have the number of figures that you need. Then look at the next digit, if its 4 or below just write the number down leaving the last digit the same. If the number is 5 or above just put the last digit up by 1.
Example 1 - 35637
To 1 significant figure (1s.f) this would be 30000
To 2s.f this would be 36000
To 3s.f this would be 35700
Example 2 – 0.004591
To 1.s.f this would be 0.005
To 2.s.f this would be 0.0046
To 3.s.f this would be 0.00459