redpearl Posted May 10, 2012 Share Posted May 10, 2012 OG Quant Review - 2nd Edition - DS-Question 46 What is the value of x^2 - y^2 ? (x square minus y square) (1) x - y = y + 2 (2) x - y = 1 / (x+y) This is an official question. OA and answer explanation is available. My query is for second condition. How can we mutiply both sides by (x+y) unless it is specified that x+y is not equal to zero or x not equal to -y. Should we assume that denominator is not equal to zero in such GMAT questions ? Quote Link to comment Share on other sites More sharing options...
Brent Hanneson Posted May 20, 2012 Share Posted May 20, 2012 OG Quant Review - 2nd Edition - DS-Question 46 What is the value of x^2 - y^2 ? (x square minus y square) (1) x - y = y + 2 (2) x - y = 1 / (x+y) This is an official question. OA and answer explanation is available. My query is for second condition. How can we mutiply both sides by (x+y) unless it is specified that x+y is not equal to zero or x not equal to -y. Should we assume that denominator is not equal to zero in such GMAT questions ? Statement 2 tells us that x-y = 1/(x+y). From this, we can conclude that x+y does not equal zero. If x+y did equal zero, then 1/(x+y) would be undefined in which case it couldn't equal some other value. So, knowing that 1/(x+y) equals some other value, it's safe to conclude that x-y does not equal zero. Cheers, Brent - GMAT Prep Now Quote Link to comment Share on other sites More sharing options...
HhjDubai Posted August 14, 2012 Share Posted August 14, 2012 IMO B. only statement 2 is needed. Quote Link to comment Share on other sites More sharing options...
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