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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## equations DS tagged by: Brent@GMATPrepNow ##### This topic has 6 expert replies and 24 member replies Goto page Junior | Next Rank: 30 Posts Joined 14 Oct 2011 Posted: 29 messages Followed by: 1 members Upvotes: 4 Math Gurus: can you please check what is wrong with my approach. Statement 2: if x=y+a then y=x-a That makes the original statement: Does (x + a)^2 = (x-a)^2? for any value of x and a, can it be true? Legendary Member Joined 15 Apr 2011 Posted: 1085 messages Followed by: 21 members Upvotes: 158 Quote: Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a the original question may ask whether a=0 or not? It may also ask given x=-7,a=2 is y=5? (or x=7,a=-2, y=-5, even we can apply modes here ... restatements could be various) with statement (1) we cannot answer if a=0 or not; also not clear if 7=! -5+2 neither -7=! 5-2 This is Not Sufficient and the answer cannot be A. statement (2) does not provide any useful information either, as we don't know if a=0 or not; neither we know if -7=! 5+2 nor 7=! -5-2 Not Sufficient. combined st(1&2): y-a=y+a must be Sufficient, as we know for sure that a=0 and then can answer the question as Yes, (x + a)^2 = y^2 p.s. I am surprised throughout the year NR's post could not find the right click for this question, even experts gave this two tries the terrible mistake of most posters here including Fabio's was using original statement from question (x + a)^2 = y^2 for plugging in statement (1) and statement (2) expressions. when we rewrite statement (1) from x+a=y into (x+a)^2=y^2 we should not forget that this is an arbitrary way of squaring both sides, we don't know the signs of (x+a) and y the same rule of thumb is noticed for many prior solutions concerning statement (2) zooki wrote: Math Gurus: can you please check what is wrong with my approach. Statement 2: if x=y+a then y=x-a That makes the original statement: Does (x + a)^2 = (x-a)^2? for any value of x and a, can it be true? _________________ Success doesn't come overnight! Master | Next Rank: 500 Posts Joined 07 Jul 2009 Posted: 160 messages Followed by: 1 members Upvotes: 1 answer A straight Legendary Member Joined 23 Dec 2011 Posted: 626 messages Followed by: 10 members Upvotes: 31 Test Date: June Target GMAT Score: 750 (A) QED _________________ Follow your passion, Success as perceived by others shall follow you Master | Next Rank: 500 Posts Joined 29 Mar 2012 Posted: 308 messages Followed by: 3 members Upvotes: 16 Target GMAT Score: 750 Answer -> A Newbie | Next Rank: 10 Posts Joined 27 Oct 2012 Posted: 8 messages Upvotes: 1 Don't noe if this approach is good but i picked numbers for this problem where x=2,a=3 so (x+a)^2=y^2 which is (2^2+2(6)+3^2)=25, so y= 5,so seeing the statements only statement (A) satisfies the condition where x= 5-3, which gives us 2 so it is sufficient whereas statement 2 gives us x= 5+3, which is insufficient. Plz correct me if this approach is correct !! ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12831 messages Followed by: 1247 members Upvotes: 5254 GMAT Score: 770 Night reader wrote: Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a Target question: Does (x + a)^2 = y^2? Statement 1: x = y - a Rearrange to get: x + a = y If two values are equal, then their squares must also be equal. That is, (x + a)^2 must equal y^2 Since we can answer the target question with certainty, statement 1 is SUFFICIENT Statement 2: x = y + a There are several sets of numbers that meet this condition. Here are two: Case a: x=1, y=1, a=0, in which case (x + a)^2 equals y^2 Case b: x=2, y=1, a=1, in which case (x + a)^2 does not equal y^2 Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT Answer = A Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12831 messages Followed by: 1247 members Upvotes: 5254 GMAT Score: 770 coolanubhav2002 wrote: Don't noe if this approach is good but i picked numbers for this problem where x=2,a=3 so (x+a)^2=y^2 which is (2^2+2(6)+3^2)=25, so y= 5,so seeing the statements only statement (A) satisfies the condition where x= 5-3, which gives us 2 so it is sufficient whereas statement 2 gives us x= 5+3, which is insufficient. Plz correct me if this approach is correct !! This approach does not work. You are assuming that the information in the target question is correct and then determining whether each statement confirms this. Also keep in mind that, if x=2 and y=3, then y can equal either 5 or -5. So, statement A may or may not work in your approach. If you're interested in learning more about how to tackle DS questions, we have a free set of videos that cover everything you need to know: http://www.gmatprepnow.com/module/gmat-data-sufficiency Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12831 messages Followed by: 1247 members Upvotes: 5254 GMAT Score: 770 zooki wrote: Math Gurus: can you please check what is wrong with my approach. Statement 2: if x=y+a then y=x-a That makes the original statement: Does (x + a)^2 = (x-a)^2? for any value of x and a, can it be true? Good question. I like how you have used the statement 2 information to rephrase the target question as "Does (x + a)^2 = (x-a)^2?" (x + a)^2 will equal (x-a)^2 when a=0. (x + a)^2 will not equal (x-a)^2 when a does not equal 0. Since (x + a)^2 may or may not equal (x-a)^2, statement 2 is not sufficient to answer the rephrased target question. Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! Master | Next Rank: 500 Posts Joined 08 Jan 2013 Posted: 171 messages Upvotes: 1 A for Answer. if a =0 then, x=y+a =y+0 x+a=y here (x+a)^2=y^2 Junior | Next Rank: 30 Posts Joined 02 Feb 2013 Posted: 16 messages Upvotes: 4 GMAT Score: 730 OA is A since x=y-a therefor we get y^2=y^2 However for statement 2 we get y+2a^2=y^2 now if a=0 then we get y^2=y^2 if a is any other number they arent equal therefore OA is A Master | Next Rank: 500 Posts Joined 16 Jul 2013 Posted: 234 messages Upvotes: 9 Target GMAT Score: 700+ obviously A Junior | Next Rank: 30 Posts Joined 23 Feb 2014 Posted: 12 messages GMAT Score: 720 Night reader wrote: Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a Direct substitution (1) (y - a + a)^2 = (y)^2 = y^2 SUFFICIENT (2) (y + a + a)^2 = (y + 2a) = y^2 INSUFFICIENT because we don't know what "a" is Master | Next Rank: 500 Posts Joined 20 Sep 2014 Posted: 164 messages Upvotes: 1 Target GMAT Score: 650 Does (x + a)^2 = y^2? (1) x = y - a (2) x = y + a (1) (y-a+a)^2 =y^2 Sufficient (2) (y+a+a)^2 = (y+2a)^2 Not sufficient Ans: A _________________ Hard work brings success! Legendary Member Joined 12 May 2015 Posted: 518 messages Upvotes: 10 Test Date: 3 Oct Target GMAT Score: 750 answer is A, we don't know value of a for statement II to be valid. • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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