Strategies, Sample Questions, and Random Ramblings.
July 19, 2015
As we showed in the previous section, ratios can be represented in percent form. As such, GMAT percents are also a way to show the relationship between numbers. First let’s cover the format of percents:
Clearly to move from percent to decimal you divide by 100. Also, being able to move interchangeably between fractions, decimals and percents will help tremendously on GMAT percents problems. Personally, I will always try to convert back to fractions as the math tends to be the easiest.
As dividing by 100 will give you a percent, if you have 100 in the denominator, the numerator is representative of the percent. This means you can covert any fraction to a percent very easily by changing the fraction to one with a denominator of 100.
Here is another example:
Where percents tend to get difficult is the translation within word problems. As there are many different ways to use percents, the GMAT will try to confuse you by flipping back and forth between percent’s various uses. Let’s look at the ways to clear the confusion.
The most common use you are going to see is “percent of.”
15 is what percent of 75?
10 of the 40 members are wearing red shirts, what percent of the total are !wearing red shirts?
What percent of a is b?
The next set you will see is changes in percent. This can be written as “percent increase”, “percent decrease”, “increased by”, “decreased by”, “percent greater”, “percent less”, “premium” or “discount”.
The basic formula you should know is this:
You will add the percent change if it is an increase and subtract if it is a decrease.
100 is increased by 20%
100 (1 + .2) = 100(1.2) = 120
100 is decreased by 20%
The key take away from the above examples is related to percent decrease. A 20% decrease is the same as 80% of the original value. Make sure you can comfortably move between the two of those.
Another way the GMAT can trick you is by asking you to calculate the percent change with two numbers or the final value after several changes. The reason this is difficult is because the base for the percent change is not always the same or easy to pick out.
The calculation for coming up with percent change is as follows:
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