This is an excerpt from a longer article by Jeff Sackmann, originally published at www.gmathacks.com. Jeff has created several valuable GMAT-preparation resources, including Total GMAT Math and Total GMAT Verbal.
The goal when finding factors of a number is to divide that number by one or more of those factors. Here are a couple of tips:
1. Start with small factors. It’s easier to divide by 2 than by 6. With just a little practice, you can divide any number by 2 or 3 in your head. If a number is divisible by 4, it may be faster to divide by 2, then divide by 2 again than to divide by 4 once.
2. Look for nearby round numbers. If you needed to divide 441 by 3, keep in mind that 441 = 450 – 9. 450 divided by 3 is 150; 9 divided by 3 is 3. 150 – 3 = 147. Alternatively, 441 = 420 + 21. By the same reasoning, the results are 140 + 7 = 147. You can apply this method with any factor, though 3 are 4 tend to be the easiest.
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