The two most important parts of successfully doing percent problems on the GMAT is to understand the language and to take the problem step by step.
The language of percentages is very specific and if you misread it, then you probably won’t get the answer right. For example, it’s important to understand how the following statements are different.
Say you have a bag of pink and blue marbles, 10 are blue 15 are pink, 5 of which are dented.
- What percentage of the pink marbles are dented?
- What percentage of the marbles are pink and dented?
Although, both one and two have very similar vocabulary, the order of the words makes them very different statements.
- asks what percent of the pink marbles are dented. This means we need to find out:
number of pink dented marbles
total number of pink marbles
This translates to 5/15 or 1/3. We multiply it by 100, to get the percent, which is approximately 33.33%.
2. asks what percentage of the marbles are pink and dented. Our numerator is still the number of pink dented marbles, bur since it is the percent of total marbles, then our denominator is the total number of marbles (45). This gives us 5/25 or 1/5, which is 20%.
Taking it step by step
The second most important element of successfully completing percent problems is taking them step-by-step. This is important for any problem type, but especially percent problems, because successive percent increases or decreases cannot be added together. What I mean by this, is that if you have a 10% increase of a number and then another 10% increase, the total increase is NOT a total increase of 20%.