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The GMAT Tip of the Week is a weekly column that includes advice on taking the Graduate Management Admission Test, which is required for admission to most business schools. Every week an instructor from a top test-prep company will share suggestions for improving your GMAT score. This week’s tip comes from Brent Hanneson, creator of GMAT Prep Now, a Web site offering on-demand videos that teach GMAT skills.
So you’re working on a GMAT question that requires you to find a certain percentage. After some work, you get to the point where you must convert 11/49 into an approximate percentage. What do you do?
Well, as always, you should check the answer choices before performing any calculations. If the answer choices are sufficiently spread apart, you can use some estimation techniques.
Let’s say that the five answer choices are as follows:
Since several answer choices are very close together, some rounding and estimation techniques may not work.
But first, an observation: A fraction with 100 in the denominator is very easy to convert to a percentage. For example, 19/100 = 19%, 72/100 = 72%, and 123/100 = 123%
To convert 11/49 to a percentage, you’ll need to find an equivalent fraction that has 100 in the denominator. In other words, you’ll find an equivalent fraction such that 11/49 = x/100.
To create an equivalent fraction, you multiply the numerator and denominator by the same value. So what number must you multiply 49 by to get 100?
If you multiply 49 by 2, you get a product of 98. So to get a product of 100, you must multiply 49 by a number a little bit bigger than 2. Let’s call this 2+.
At this point, multiplying numerator and denominator by 2+ yields the following equation: 11/49 = (11)(2+)/(49)(2+). The product (49)(2+) in the denominator equals 100, and the product (11)(2+) in the numerator equals 22+ (a number a little bit bigger than 22).
So, 11/49 = (22+)/100 = 22+%, which is a little bit more than 22%. When you check your answer choices, only answer choice C fits the bill. It must be the correct answer.
Let’s try one more example.
To convert 15/34 to a percent, you’ll first find an equivalent fraction with 100 in the denominator. In other words, you need to find an equivalent fraction such that 15/34 = x/100.
To create this equivalent fraction, take 15/34 and multiply the numerator and denominator by 3- (a number a little bit smaller than 3), to get 15/34 = (15)(3-)/(34)(3-). When we simplify, we get 15/34 = (45-)/100 = 45-%, which is a little bit less than 45%.
Brent Hanneson, the creator of GMAT Prep Now, has worked in the field of education for most of his career. He has taught courses at three different test-prep companies and created comprehensive GMAT and GRE courseware packages used by the University of British Columbia and 12 other universities across North America.