rseeker2 wrote:
x-y/x+y > 1
x-y > x+y
Your mistake is in the line above: you don't know whether x+y is negative. If x+y is negative, when you multiply both sides by x+y, you'd need to reverse the inequality.
This is probably the most common trap in GMAT inequality questions. If you are ever tempted to multiply or divide on both sides of an inequality by an unknown, *always* ask yourself: do I know the sign of this unknown? If you don't know whether the unknown is positive or negative, you can't multiply or divide by it, since you won't know what direction the inequality should face afterwards.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com
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