Land Your Score: Mental GMAT Math Tips

by on April 12th, 2017

1No calculator on the GMAT? No problem. With an arsenal of mental GMAT math tricks at your disposal, you won’t need no stinkin’ calculator. Here are some ways to get ahead of the curve in Quantitative Reasoning arithmetic.

GMAT math multiplication hacks

The testmaker knows we all learned our multiplication tables through multiples of 12. So what are you likely to see on the GMAT? Multiples of 13, 14, and 15. Add these to your list of things to learn (really you only need work on 13, since 14 is two 7s and 15 is three 5s) to save yourself some scribbling on test day.

Other multiplication tips include this trick for remembering multiples of 5: Cut in half and add a 0. If you need to multiply 516, for example, imagine you have 0.5 instead of 5. One-half of 16 is 8, so just add back the 0 to get 516=80.

When you need to multiply large numbers, don’t multiply right away. Chances are good you will be able to cancel or reduce one of the factors in a later step of the solution. I always keep the “unmultiplied” factors in parentheses until I am sure they must be multiplied. This is a simple example but shows what I mean: 12x=(12)(15); I will cancel out the 12s without multiplying. Saving a few seconds here gives me precious time I may need later.

Answer choice timesavers

Also when multiplying, remember to check the units (or tens) digit instead of multiplying all the way out: If a question’s answer choices end in different digits, such as 1,105, 2,344, 3,432, 4,561, and 5,329, you can stop your final multiplication step when you see the units digit. If they end in the same digit but are all different tens digits, such as 1,100, 2,340, 3,430, 4,560, and 5,320, you will know when you have the last two digits of the product which choice is the correct answer.

Likewise, instead of dividing two numbers all the way out, you often can identify the correct answer based on the first or first two numbers on the left side.

An easy way to divide by 5 is to first divide by 10, then multiply by 2. So instead of dividing 180 by 5, divide by 10 (18010=18) and multiply by 2 (182=36). Thus, 1805=36.

Shortcuts to simplifying percentages

To simplify a fraction with denominator 9, simply multiply the numerator by 0.111. So 19=0.111, 29=0.222, etc., all the way through to 89=0.888. Just remember to round up if needed, as those are all repeating decimals.

Remember that any percent that ends in 0 can be calculated by finding 10% and then multiplying by the non-zero number(s). For example, 60%(130)=10%(130)6, or 136. And if you’ve followed my first tip above, you know your multiples of 13 and know the answer here is 78.

My very favorite mental math tip of all is this percent tip, which allows me to solve complicated percents with almost no effort:  x% of y = y% of x. You can move the decimal to whichever number is easier for you to work with: 28%(25)=25%(28).

If you’re like me, you have no idea at a glance what 28% of anything is. But 25% is simply 14, which is easy math: 284=7 and 28%(25)=7 as well.

Master these little tricks when you don’t have enough time to fully prep but want to keep your GMAT skills sharpened. They save time and boost confidence on Test Day.

How would you score if you took the GMAT today? Find out with a free practice test and review.

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