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GRE Math Practice: Snowpocalypse Edition

February 17, 2014 by

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If you were unlucky enough to be living in a part of the United States that got pummeled with winter weather this past week – and that would be most of the country – then at the very least I hope you were able to crack your GRE books and get in some quality studying. During your GRE math practice, you may have encountered some questions that asked you to calculate the percent change between two values. These questions are relatively common on the GRE, and for most students, they aren’t that difficult. However, be on the lookout for a type of question that looks similar to a percent change question, but is actually slightly different: the question that asks what a new value is as a percent of the original.

Even expert test-takers need to be on the lookout for these tricky questions  – not because they’re difficult, but because it can be easy to overlook the specific task the question asks for. While these tend to show up in Data Interpretation questions, it’s possible you’ll see them elsewhere on the test. Let’s take a look at a chart and a couple of questions now.

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Question 1:  As a percent, how much more snowfall did Chicago receive in 2013 than in 2012? 

Notice that the question specifically asks for a percent, and it asks for how much more snow fell in 2013. In other words, it’s asking for the amount of change that occurred from one year to the next. This is a classic percent change question, and you’ll attack it in the same way you attack every other percent change question: find the amount of change, and compare it to the original. Here, the difference is 5 inches, and the original amount of snowfall was 30 inches, so:

5/30 = 17%.

Now let’s take a look at a very similar, but ever-so-slightly different question.

Question 2: As a percent of the amount of snow that fell in New York in 2012, how much snow fell in New York in 2013?

Tricky, tricky! This question doesn’t actually ask you to find the difference in snowfall between two years; instead, it asks you to compare two values and generate the correct answer as a percent. Here, the amount of snowfall in New York in 2013 was 25 inches, while in 2012 it was 20 inches.

25/20 = 5/4 = 125%

As a percent, New York received 125% the amount of snow that it received in 2012.

When faced with a percent question that asks you to compare the difference between two values, be careful. While these questions often ask you to find the percent change from one value to the next, you cannot assume that every question will do so.

Questions? Ask me in the comments.

 

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