Rounding Decimals for Dummies

Rounding Rules

It amazes us here at the Antisocial Network just how quickly some people forget the basics when they no longer use them. Now that everyone has a smart phone with a calculator, for instance, no one can remember how to calculate 15% (or 20%) of a restaurant bill for the tip. This loss of knowledge is the basis for the syndicated quiz show "Are You Smarter than a Fifth Grader?" Face it: the kids just studied world geography, while it's been 20-plus years since you needed to know the capital of Spain (Madrid, in case you wondered). Well, nothing has changed for the freelance dumbasses at eHow.com, bull-tossers like William D. Gardlock (wannabe foodie and business major) who apparently forgot "How to Round Decimals," now found at Sciencing.com.

You know the drill, right? You look at the value of the next number after the target decimal place and round accordingly: up if it's greater than 5, down if it's less than 5, and to the even number if it's exactly 5. Gardlock gets that bit right, except for the "exactly 5" part:

"If it is under 5, round down; if it is 5 or over, round up."

...which is what you teach fourth-graders who don't yet understand the difference between even and odd. Where Bill gets fouled up (besides his condescending style: "Learn how to round down.") and his content editor doesn't help matters at all is in the presentation of his examples. For rounding up, he says to

"Take 2.2 for example. Look at the number to the right of the decimal point; this is the number we want to round. When the number you want to want to round is less than 5, you will round down, so the answer would be 2.0 Another example: 10.3 becomes 10.0." ...while for rounding down, Gardlock's examples are "Take 4.6 for example. Again you want to look at the number to the right of the decimal point. This number would be 5.0, because when the number you want to round is 5 or more, you will round up. This works with any decimal. Another example: 1.473 becomes 1.5"

See Bill's mistakes there? Well, we did! We wondered, in what mathematics does 2.2 round down to 2.0? 10.3 round to 10.0? 4.6 round up to 5.0? Gardlock completely ignores the purpose of rounding decimals: to reduce the number of (significant) digits – you're rounding those numbers to the nearest integer, dummy! Not only that. his last example ("...1.473 becomes 1.5...") fails to address the concept of the number of decimal places: 1.473 could round up to 1.5, but it could also round down to 1.47 or 1 (note that it doesn't round to 1.0).

Such are the hazards of asking a foodie and business major ten or more years removed from elementary math (and assiduously avoiding "hard" college classes like algebra) to help you with fifth-grade arithmetic. For his lousy answer (and condescending style) we hereby present Gardlock the Dumbass of the Day award. Round that off, sucker!

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