• NEW! FREE Beat The GMAT Quizzes
    NEW! FREE Beat The GMAT Quizzes
    NEW! FREE Beat The GMAT Quizzes
    Hundreds of Questions Highly Detailed Reporting Expert Explanations TAKE A FREE GMAT QUIZ
  • 7 CATs FREE!
    If you earn 100 Forum Points

    Engage in the Beat The GMAT forums to earn
    100 points for $49 worth of Veritas practice GMATs FREE

    Veritas Prep
    VERITAS PRACTICE GMAT EXAMS
    Earn 10 Points Per Post
    Earn 10 Points Per Thanks
    Earn 10 Points Per Upvote
    REDEEM NOW

equations DS

This topic has 6 expert replies and 24 member replies
Goto page Previous Next
Junior | Next Rank: 30 Posts Default Avatar
Joined
14 Oct 2011
Posted:
29 messages
Followed by:
1 members
Upvotes:
4
Post
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?

  • +1 Upvote Post
  • Quote
  • Flag
Legendary Member Default Avatar
Joined
15 Apr 2011
Posted:
1085 messages
Followed by:
21 members
Upvotes:
158
Post
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!

  • +1 Upvote Post
  • Quote
  • Flag
Master | Next Rank: 500 Posts Default Avatar
Joined
07 Jul 2009
Posted:
160 messages
Followed by:
1 members
Upvotes:
1
Post
answer A

straight

  • +1 Upvote Post
  • Quote
  • Flag
Legendary Member
Joined
23 Dec 2011
Posted:
626 messages
Followed by:
10 members
Upvotes:
31
Test Date:
June
Target GMAT Score:
750
Facebook Logo
Post
(A)
QED

_________________
Follow your passion, Success as perceived by others shall follow you

  • +1 Upvote Post
  • Quote
  • Flag
Master | Next Rank: 500 Posts
Joined
29 Mar 2012
Posted:
308 messages
Followed by:
3 members
Upvotes:
16
Target GMAT Score:
750
Post
Answer -> A

  • +1 Upvote Post
  • Quote
  • Flag
Newbie | Next Rank: 10 Posts Default Avatar
Joined
27 Oct 2012
Posted:
8 messages
Upvotes:
1
Post
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 !!

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post
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 – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Sign up for our free Question of the Day emails
And check out all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!

GMAT/MBA Expert

Post
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 – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Sign up for our free Question of the Day emails
And check out all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!

GMAT/MBA Expert

Post
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 – Creator of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

Sign up for our free Question of the Day emails
And check out all of our free resources

  • +1 Upvote Post
  • Quote
  • Flag
GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
Master | Next Rank: 500 Posts Default Avatar
Joined
08 Jan 2013
Posted:
171 messages
Upvotes:
1
Post
A for Answer.

if a =0

then, x=y+a
=y+0

x+a=y

here (x+a)^2=y^2

  • +1 Upvote Post
  • Quote
  • Flag
Junior | Next Rank: 30 Posts Default Avatar
Joined
02 Feb 2013
Posted:
16 messages
Upvotes:
4
GMAT Score:
730
Facebook Logo
Post
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

  • +1 Upvote Post
  • Quote
  • Flag
Master | Next Rank: 500 Posts
Joined
16 Jul 2013
Posted:
234 messages
Upvotes:
9
Target GMAT Score:
700+
Post
obviously A

  • +1 Upvote Post
  • Quote
  • Flag
Junior | Next Rank: 30 Posts Default Avatar
Joined
23 Feb 2014
Posted:
12 messages
GMAT Score:
720
Post
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

  • +1 Upvote Post
  • Quote
  • Flag
Master | Next Rank: 500 Posts
Joined
20 Sep 2014
Posted:
164 messages
Upvotes:
1
Target GMAT Score:
650
Facebook Logo
Post
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!

  • +1 Upvote Post
  • Quote
  • Flag
Legendary Member Default Avatar
Joined
12 May 2015
Posted:
518 messages
Upvotes:
10
Test Date:
3 Oct
Target GMAT Score:
750
Post
answer is A, we don't know value of a for statement II to be valid.

  • +1 Upvote Post
  • Quote
  • Flag
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • The Princeton Review
    FREE GMAT Exam
    Know how you'd score today for $0

    Available with Beat the GMAT members only code

    MORE DETAILS
    The Princeton Review
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep

Top First Responders*

1 Jay@ManhattanReview 69 first replies
2 Brent@GMATPrepNow 66 first replies
3 GMATGuruNY 42 first replies
4 Ian Stewart 25 first replies
5 Scott@TargetTestPrep 15 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

Most Active Experts

1 image description Scott@TargetTestPrep

Target Test Prep

200 posts
2 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

92 posts
3 image description Max@Math Revolution

Math Revolution

91 posts
4 image description Jay@ManhattanReview

Manhattan Review

76 posts
5 image description GMATGuruNY

The Princeton Review Teacher

64 posts
See More Top Beat The GMAT Experts