The Importance of “Of”

(This is one of a series of GMAT tips that we offer on our blog.)

One of the smallest and least noteworthy words in the English language, the word “of” is crucial to your success on the GMAT, on both the quantitative and verbal sides of the exam. Accordingly, it is of great importance that you recognize these two common appearances of, and traps set by, the word “of“:

1) Percentages:

The most common error that examinees make on percentage-based questions is that they take the percentage of the wrong number. Asking yourself “of what?” is the easiest way to ensure that you never make this mistake. Take, for example, the problem:
If a car dealership wants to earn \$20,000 from the sale of a new car, and wants that price to reflect a 50% discount to the customer, where should the dealer mark the retail price?

Many students will take 50% of 20,000 and add that to the original number, coming up with an answer of \$30,000. That is incorrect – ask yourself “50% of what”? A discount is always taken off of the retail price, so this problem should correctly be set up to reflect that \$20,000 is equal to 50% off of the retail price. Mathematically, that is: 20,000 = Retail – (50/100) Retail, and the retail price works out to be \$40,000.

Be careful with percentages – asking yourself that crucial question “of what?” will help you to avoid commonly catastrophic errors

2) Sentence Correction

In Sentence Correction problems, the word “of” is commonly employed as a modifier, which the GMAT often throws in to lengthen sentences and distract you from subject-verb agreement errors. Consider the following items:

The number of applicants to business schools are increasing given the current economic climate.

The House of Representatives are meeting this week to continue working on an education bill.

In either case, the subject is actually the singular noun before the word “of” – “of applicants to business schools” just tells us “which number?”, and “of Representatives” simply indicates “which House?”. The writers of the GMAT know that examinees are often unsure of which noun to choose as the subject; by using the word “of” to set up modifiers with multple nouns, the writers can exacerbate this problem. If you are aware of, and searching for, these modifiers, you can quickly avoid these common mistakes.

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