Here are some practical tips on how to know when (as well as how) and when not to round off:
- Check the instruction page (if you are writing a test), it will tell how you need to round of for the question paper as a whole. It will most likely say something like, “Round off to two decimal places, unless otherwise stated” or “Round off your answers appropriately to the given context, unless otherwise stated”.
- “Unless otherwise stated” means that you must still check each question as a specific question may want you to round off to one decimal place, for example.
- “According to the context” means that you need to think about how you need to round off your answer according to the specific question you are answering.
Let’s look at a few examples to illustrate what I have just said:
Example 1: You have been asked to share R200 between 3 people. So your calculation would be 200/3 = 66,66666666666…. Your answer is in rands so you know to round off to two decimal places (because money has two decimal places). Therefore, your answer would be R66,67.
Example 2: You have been asked to calculate the speed of a bicycle that travelled 10km in 3 hours. But at the end of the question it specifically said “correct your answer to one decimal place”. So your calculation would be 10/3 = 3,333333333…… Therefore your answer would be 3,3km/hr. Remember that you would round off to two decimal places if the question hadn’t specifically asked for you to round off to one decimal place.
Example 3: You have been asked to calculate how many 30cm rulers could be placed horizontally along a table that had a length of 145cm. Your calculation would be 145/30 = 4,833333333…. Remember that this is the number of rulers so you must round off to a whole number (as you can’t have a piece of a ruler placed on the table). According to the rules of rounding off, your answer would become 5 rulers. However, 5 rulers would not fit along the length (5 x 30cm = 150cm and the table is only 145cm in length). Therefore, you would “round down” and your answer would be 4 rulers.