Dividing the top and bottom by two gives you 42/8 by another two results in 21/4. Instead of doing long division and having to solve to two decimal places, simplify the fraction one factor at a time. The second method is: factor, factor, factor. But the end result-a denominator canceling out-is a very common occurrence in actual GMAT questions. My example above may seem artificial, and it's true, I did just invent it for the purpose of this tip. In that case, not only did you save yourself the trouble of long division, you also made the second step easier! 135 times 2 is much simpler than 19 2/7 times 14. You probably see where I'm going with this: 7 is a factor of 14, so rather than multiplying 135 by 14, eliminate the denominator and multiply 135 by 2. In other words, you're asked to multiply the day rate by 14. Perhaps the question ends up by asking, "if the factory produces widgets at a constant rate seven days per week, how many widgets does it produce in two weeks?" If you had a calculator, it'd be easy to convert that to 19 2/7, but on the GMAT it's not worth the time. Avoid the temptation until there's no alternative.įor example, let's say you're working a problem about a factory producing widgets, and you deduce that it's producing 135/7 widgets per day. If, after the first step of a problem, you come out with a fraction, say 135/7, it may be tempting to convert that to a decimal or compound number.
The first, simplest way to avoid long division on the GMAT is this: Don't calculate until you have to. If you're doing a lot of tedious work on a single problem, you're almost certainly missing out on a more efficient method. This obviously applies to much more than just long division, but it's particularly important to remember here. Business schools aren't looking for calculators, they're looking for students who can solve problems effectively while under pressure. Luckily, the writers of the GMAT realize that too. You're not going to business school so that you can become a clerk for an 19th-century accounting firm. If there's a faster way, you should be using it. Even if you make it through the several steps of a single long-division problem without a careless mistake, you've probably spent 20 seconds or longer doing it-a big chunk of the time you should allot for that question. You don't need me to tell you that time management is key on the GMAT. Most people have divided with a calculator for their entire adult life.ģ. My apologies if you're a long-division whiz, but the vast majority of students I've worked with are about as comfortable as I was when I started teaching middle-school kids. Instead of just one or two steps (like, say, multiplying two-digit numbers), long division can include several steps, each of which is a chance to make a careless error.Ģ. Long division is the worst form of tedious calculation. It may feel like there's no rhyme or reason behind the mistakes you make, but there is definitely a way to cut down on them: do less tedious math. Everybody wants to avoid careless errors, yet we all seem to make them. Three problems with long division on the GMATġ. You will, however, find yourself in several situations where you want to set up a long-division problem, despite the fact that it's not a skill you've practiced very much since you were 12 or 13 years old, and one that, even at its best, is mighty-time consuming. Of course, you can't use a calculator on the GMAT. It was understandable: I hadn't taken a math class in years, and when I did have to divide, a calculator was always at hand.
#How to do division fast how to#
When I was 19 years old and started my test-preparation career working with middle schoolers on a high-school admissions exam, I got a nasty jolt: I had completely forgotten how to do long division.
Subscribe to GMAT Hacks via RSS or Email. Never Do Long Division Again March 17, 2010
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