GRE Math Help – Fractions, Decimals and Percents
A Guide to Understanding Simple Yet Necessary Functions for the GRE
Nov 12, 2009
It’s no secret: the GRE math section (or Quantitative Reasoning, as it’s referred it on the test) will be difficult for a good deal of test-takers. However, by having a solid grasp on the basics – what many students learn as early as fourth grade – students can have more confidence in themselves when it comes to the tricky questions that will be presented to them.
Fractions, decimals, and percents are seen often in the GRE math sections, so before taking the test, students should try to get a good grasp on them so they can convert one to the other quickly and efficiently. And because these three ways of expressing quantities are synonymous, becoming comfortable with them is of dire importance.
Converting Fractions to Decimals to Percents
It’s simplest to start with percents. Converting percents to decimals is easy: simply take the percent and move the decimal two places to the left. For instance, 90% would be 0.90, and 26% would be 0.26. 9% becomes 0.09 and .9% becomes 0.009. Move the decimal point two places to the right to convert a decimal to a percent (try the above examples backwards).
To convert a percent to a fraction, divide the percent by 100 after dropping the percent sign. The easiest way to remember this is to think of 100% as 1/1, or 1. 50% is equal to 50/100, or ½. 730% becomes 730/100. Simplified, 730% becomes 7 and 3/10. Remember to simplify any fractions, if possible.
Rewriting a fraction as a percent requires multiplying by 100. 3/8, for instance, becomes 300/8, simplifies to 75/2, and is finally written as 37 and ½ %. Practice makes perfect, as the saying goes, so be sure to get these conversions down as solidly as possible.
Common Conversions
It may be a good idea to closely familiarize with the most common percentages, decimals, and fractions (and their conversions) so working through problems can come more quickly. Below are a few of the most common expressions on the GRE, listed as percent to decimal to fraction.
- 50% is 0.50 is ½
- 25% is 0.25 is ¼
- 75% is 0.75 is ¾
- 10% is 0.10 is 1/10
- 30% is 0.30 is 3/10
- 70% is 0.70 is 7/10
- 90% is 0.90 is 9/10
- 33 1/3% is 0.33 1/3 is 1/3
- 66 2/3% is 0.66 2/3 is 2/3
- 16 2/3% is 0.16 2/3 is 1/6
- 83 1/3% is 0.83 1/3 is 5/6
- 20% is 0.20 is 1/5
- 40% is 0.40 is 2/5
- 60% is 0.60 is 3/5
- 80% is 0.80 is 4/5
- 12 ½% is 0.125 is 1/8
- 37 ½% is 0.375 is 3/8
- 62 ½% is 0.625 is 5/8
- 87 ½% is 0.875 is 7/8
This reference works well as a chart for a study tool. Once put into chart form, clear patterns become apparent, and it’s these patterns that will make it easier to memorize the conversions. The first few conversions should be easy, as they are often made on a daily basis. Quarters, for instance, are easier than eighths or sixths.
Notice with the tenths-conversions (10, 30, 70, and 90%), the only percents that convert to the tenth fractions are ones that can’t be simplified any further. 30% converts to 3/10, but 50% converts to 5/10, which simplifies to ½.
There are only two thirds-conversions above, which are also obvious to many students (three parts of 100), and are listed above as fractions to avoid the ongoing threes and sixes with the decimal points.
The eighths-conversions present an easy pattern to remember. Each eighths-conversion percent and decimal form ends in 5, or ½. This can be helpful when trying to memorize the chart.
Though these tips and conversions seem elementary (and indeed, they are), many students going in to take the GRE haven’t had to convert fractions to decimals, or decimals to percents, since freshman core classes. Memorizing the most common conversions can make complicated problems easier by eliminating the perky conversion steps.
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