Practice GMAT Data Sufficiency Question

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Is 13N a positive number?
  1. -21N is a negative number
  2. N2 < 1
Correct Answer: A
  1. Simplify the question:
    Since multiplying a number by 13 does not change its sign, the question can be simplified to: "is N a positive number?"
  2. Evaluate Statement (1) alone.
    1. Write out algebraically:
      -21N = negative
      21N = positive {divided by -1}
      N = positive
    2. Since N is a positive number, 13N will always be a positive number.
    3. Statement (1) alone is SUFFICIENT.
  3. Evaluate Statement (2) alone.
    1. Any time you are dealing with a number raised to an even exponent, you must remember that the even exponent hides the sign of the base (e.g., x2 = 16; x = 4 AND -4).
    2. Solve the inequality:
      N2 < 1
      -1 < N < 1 {take the square root, remembering that there is a positive and negative root}
    3. Since N can be both positive (e.g., .5) or negative (e.g., -.5), Statement (2) is not sufficient.
    4. Statement (2) alone is NOT SUFFICIENT.
  4. Since Statement (1) alone is SUFFICIENT but Statement (2) alone is NOT SUFFICIENT, answer A is correct.

Return to the list of practice GMAT data sufficiency questions.