Practice GMAT Problem Solving Question

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f(x) = -5x197-8x248+1; f(-1) = ?
Correct Answer: C
  1. To determine f(-1), we must first know (-1)197 and (-1)248. You should never multiply out lots of numbers.
  2. Instead, look for a pattern:
    (-1)1=-1
    (-1)2=+1
    (-1)3=-1
    (-1)4=+1
    ...
    (-1)(odd number)=-1
    (-1)(even number)=+1
  3. This means (-1)197=-1 since 197 is odd and (-1)248=+1 since 248 is even.
  4. This pattern simplifies the equation to:
    -5(-1) - 8(1) + 1, which equals 5 - 8 + 1, or -2.
    Thus, C is the correct answer.

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