How to Round Numbers (Part 1)

The Math Dude: Quick & Dirty Tips to Make Math Simpler

Scientific American presents Math Dude by Quick & Dirty Tips. Scientific American and Quick & Dirty Tips are both Macmillan companies.

At some point in your life, you were most likely taught how to round integers and decimal numbers to some specified number of digits or decimal places. And you probably discovered that this process is, thankfully, fairly straight-forward.

But even though it is a relatively easy task, it turns out there are a few details about rounding that make it a touch trickier than you might at first think. What are those tricky little bits that you really ought to know about? And how do you round in the first place? Those are exactly the questions we'll be answering over the next few weeks!

Why Is Rounding Useful?
Imagine this: You need to put together a monthly budget for your company that sells novelty T-shirts depicting cats dressed as baristas. You decide that the best way to get started is to take a look at all of your company's expenses over the past 6 months, and to calculate the average monthly cost of each kind of expense. Perhaps your average cost for the shirts themselves turns out to be \$1,024, the average cost of shipping turns out to be \$512, and the average monthly cost of all the fancy coffee drinks you buy to inspire you when drawing your barista cats turns out to be \$128.