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Rounding Whole Numbers


Rounding is a useful tool in math, as it allows us to get a rough sense of a number to do quick mental math. For example, if you are hosting a party for 19 people, and you want to buy enough small cakes for everyone at the party (you assume 3 per person will be enough), you can round 19 guests to 20, which makes calculating the total number of small cakes much easier (since 20 x 3 is easier to work out than 19 x 3).



To round a whole number, you first have to decide how precise you need to be. If you only need a rough estimate, you can be very broad with your rounding. If you need a more detailed estimate, you need to be a bit more specific.

For example, if you are trying to work out what to budget to buy a new pair of shoes, it doesn't matter if you estimate a pair of shoes to be 50or50 or100. If, however, you want to work out how much wallpaper to buy to decorate a room, the difference between 50 square yards and 100 square yards is too big.

In order to round a whole number, you need to turn it into a number with a zero at the end. If you need to be quite precise, then usually one zero will work. If you don't need to be precise, then you can round to a number that has a single digit followed by zeros.

For example, let's say you have money in a savings account totaling 468.00Therearetwodifferentlevelsofroundingyoucando.Ifyouwanttobequiteprecise,butstillround,youcouldsayyouhaveroughly468.00 There are two different levels of rounding you can do. If you want to be quite precise, but still round, you could say you have roughly470. If you don't need to be precise, you can round to $500.

The key question with rounding is how precise you need to be. That will determine which 'landmark number' you need to get to.


Round the number 189189 to the nearest tenten.
paper.numberWithRoundingDigit(189,1);paper.numberWithRoundingDigit(189, 1);
paper.rounding(189,1,2);paper.rounding(189, 1, 2);
189190189 \approx 190

Rounding Whole Numbers Worksheets (PDF)