GMAT Math: Picking Numbers

Written by Kelly Granson. Posted in GMAT Study Guide

GMAT math picking numbersWhen you face a GMAT problem that contains an abundance of unknowns and variables, you do not necessarily need to perform all the entangled operations that would lead to the correct answer. If the problem does not require you to find a solution or the exact value of one of the variables, you can lower the hurdles in your quantitative section by using a technique known as "picking numbers" or "plugging in numbers."

In practice, picking numbers means that you replace the unknowns or variables with some numbers that are easy to handle, and then test your answer choices using these numbers. This strategy has proven helpful because working with arithmetic problems is easier for most people than handling algebra is. Plugging in numbers moves you from an abstract problem to a more concrete one, thus making it easier and less intimidating.

The procedure for plugging in numbers is a two-step process.

Step 1: Replace the unknowns or variables in the problem with numbers that satisfy the conditions of the problem, and then perform the necessary calculations.

Step 2: Test the answer choices using the same numbers, and compare your outcomes with the result you got in Step 1 to determine which option yields a matching answer.

To be sure, plugging in numbers is no panacea for the entire quantitative section of GMAT, but it will be helpful in four instances:

  • If the answer choices are not concrete numbers but feature one or more variables introduced in the question, plug in numbers that represent each of your unknowns.
  • If the question is based on undefined values or fractions of the unknown rather than specific numbers, pick values to represent the unknowns, making your calculations more concrete and thus more manageable.
  • If the question refers to number properties (factors, multiples, odds or evens, negative or positive numbers and so on), plug in numbers that comply with the parameters in full, keeping in mind that some numbers' properties are tricky. For instance, zero is neither positive nor negative; 2 is the only even prime number. GMAT creators, who often set traps for test-takers, are well aware of the number-picking technique, so steer clear of plugging 2 into number properties questions if you don't want to get caught in one of their traps. In some cases, you might need to plug in several sets of numbers to eliminate all the incorrect answer options.
  • If a question involves percentages of an unknown value, it is conventional to substitute 100 for the unknown value (since 100% makes up the whole) and perform your manipulations based on the concrete results.

Whichever type of question you are working on, make sure that you read it carefully and pay attention to all the criteria given; this can have a dramatic effect on the outcome. On the other hand, be careful to avoid making assumptions not directly supported. For example, if your question states that x, y, and z are consecutive numbers, you can't assume that x<y<z or x>y>z. Any assumptions that you make must stem directly from the question formulation. Finally, plug in simple, manageable numbers. Forget about 23s or 169s: the objective of this strategy is to simplify questions, not complicate them. Nice, easy numbers like 2, 3, and 4 usually work quite well.

By plugging real numbers into abstract algebraic problems, you make your task easier by eliminating confusing values and ambiguous properties, leaving you a very concrete problem to manage. This will reduce the time and nerves required to cope with the quantitative section, which (along with greater accuracy) translates into an improved GMAT score. So take advantage of this strategy for achieving the best result you can. Plug in!

 

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