GMAT Math : Unnecessary information

Part of the skill in solving GMAT quant questions rapidly and accurately lies in knowing which information is unnecessary to solving the question.

Let’s use an example to illustrate the point :

What is the value of x4 + |x – 5| + x8?

  1. |x| = 2
  2. x2 – 5x + 6 = 0

Statement (1)

|x| = 2 entails x = +2 or – 2. We know the magnitude of x is 2 and hence we can solve the question expression

Statement (2)

The given expression can be simplified as (x – 3) (x – 2) = 0. Hence, x = 2 or 3. With different magnitudes of x we cannot solve the original question expression to come to one value. Hence insufficient information.

We go with option (A)

Key learning: Note in the original question expression, all terms are either absolute values or even powers. This means all we have to do is determine the ‘magnitude’ of x to solve the equation. The ‘sign’ of x becomes unnecessary as ultimately all terms in the equation will end up positive.

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