GMAT Tips from Veritas Prep

Reduce, Reuse, and Recycle—Part II


Reduce, Reuse, and Recycle—Part II

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This tip on improving your GMAT score was provided by David Newland at Veritas Prep.

Before you start reading, make sure to read Part I of this series.

Reuse means to find a way to use something in its current form, so that no energy is required to remake the item. If you keep a glass jar and store something else in it, you get a second use from the item at no additional cost.

Reuse is also a great strategy on the GMAT. If you can get a second use for no extra time or energy, you are working efficiently.

Reuse on Data Sufficiency
Data Sufficiency is one of the best areas to apply the concept of “reuse.” For any data sufficiency problem where you actually use values to test the statements, you should be on the lookout for values you can use with each statement. If a particular value is acceptable to statement 1, try that value with statement 2 as well. This is reusing at its best.

Try the following problem:

Is x divisible by 24?
x is divisible by 6
x is divisible by 4

This problem is an excellent example of reusing numbers on Data Sufficiency. There are different ways to approach this problem, including breaking 24 down into the prime factors before approaching the statements. The technique we are going to explore now is one that many test takers will adopt—plugging in values for x.

To evaluate the first statement, we want to see if we can use a value for x that is divisible by 24 and another value for x that is not divisible by 24. Statement 1 gives the constraint that the values must be divisible by 6, so we could not use, for example, 15 as a value for x since this does not divide evenly by 6. Statement 1 allows only multiples of 6, because those are the only numbers that divide evenly by 6.

The first value to plug in for x is 24, which does divide by 6 and so is an acceptable value. It also, of course, divides by 24. So this number gives us an answer of “Yes” to the question, “Is x divisible by 24.” Now we want to put our focus on getting an answer of “No. x is not divisible by 24.” Remembering that x must be divisible by 6, we can choose 12 as a number that does divide by 6, but not by 24.

Since we have both a “No” and a “Yes,” statement 1 is not sufficient.

It is in evaluating statement 2 that the concept of reuse comes into play. While testing statement 2 to see if it is sufficient, we will try to use as many of the values we tested as possible. For this particular problem, you can see that 24 works for statement 2 as well. It is divisible by 4, and it is divisible by 24. So this is an answer of “Yes.” The value that gave us a “No” for statement 1 works here as well; 12 is divisible by 4 and is not divisible by 24.

So each of the values that worked with statement 1 also worked with statement 2. Therefore, not only is each statement not sufficient alone, but we already know that the statements are not sufficient together, since the values of 24 and 12 clearly satisfy both statements and give an answer of “Yes” and “No” to the question.

Reusing saves the time and energy of coming up with additional numbers, but more importantly, it also gives you values that satisfy both statements, so that if you need to evaluate both statements together you can do so more efficiently.

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