Practice GMAT Data Sufficiency Question
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Is 13N a positive number?
- -21N is a negative number
- N2 < 1
Correct Answer: A
- 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?"
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Evaluate Statement (1) alone.
- Write out algebraically:
-21N = negative
21N = positive {divided by -1}
N = positive
- Since N is a positive number, 13N will always be a positive number.
- Statement (1) alone is SUFFICIENT.
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Evaluate Statement (2) alone.
- 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).
- Solve the inequality:
N2 < 1
-1 < N < 1 {take the square root, remembering that there is a positive and negative root}
- Since N can be both positive (e.g., .5) or negative (e.g., -.5), Statement (2) is not sufficient.
- Statement (2) alone is NOT SUFFICIENT.
- Since Statement (1) alone is SUFFICIENT but Statement (2) alone is NOT SUFFICIENT, answer A is correct.
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