BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Algebra

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
Legendary Member
Posts: 2326
Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members
Thanked: 173 times
GMAT Score:710

by gmatmachoman » Mon Jun 21, 2010 9:26 am
mehulv wrote:Given that A = 3y + 8x, B = 3y - 8x, C = 4y + 6x, and D = 4y - 6x, what is the value of x*y?

1. AB + CD = -275
2. AD - BC = 420
Its a bit lengthy calculative one..still it may pop up !!

Pick B

st 1:
apply those values of A,B,C,D

we will get y^2 - 4X^2 = -11

x*y can take any number of values .Insufficient

st 2


apply those values of A,B,C,D

we will get 28 X*Y = 420

X*Y =15

Pick B..Move on!!
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 509
Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members
Location: Irvine, CA
Thanked: 199 times
GMAT Score:750

by tpr-becky » Mon Jun 21, 2010 11:57 am
this is a quadratics problem - you have to solve each of the quadratics using FOIL and then see how they relate to each other, a calculation intensive problem but certainly doable if you recognize the method from the begining.
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 2326
Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members
Thanked: 173 times
GMAT Score:710

by gmatmachoman » Tue Jun 22, 2010 1:01 am
tpr-becky wrote:this is a quadratics problem - you have to solve each of the quadratics using FOIL and then see how they relate to each other, a calculation intensive problem but certainly doable if you recognize the method from the begining.
@becky--- My query is will these sort of questions pop up in real test???What I see, is every problem has some logic/hidden fundae which we are forced to unplug.

Whereas in calculative ones, I don't think we apply logic..so what are the chances???
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 509
Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members
Location: Irvine, CA
Thanked: 199 times
GMAT Score:750

by tpr-becky » Tue Jun 22, 2010 6:53 am
This question is plausible - it isn't the normal type of question we have been seeing but the GMAT seems to be shifting to include more problems that you actually have to calculate - although most of these have been in the inequalities. You still don't have to solve the entire thing until you get to teh end of B becuase it is clear that statemetn 1 will get you two squares by looking at the law of quadratics (x-y)(x+y)=x^2 - y^2. This problem is good to study becuase it helps with the Quadratic reasoning.
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Legendary Member
Posts: 748
Joined: Sun Jan 31, 2010 7:54 amFollowed by: 3 members
Thanked: 46 times

by outreach » Tue Jun 22, 2010 11:42 am
B

option1

AB = (3y + 8x)(3y - 8x) = 9y2 - 64x2
CD = (4y + 6x)(4y - 6x) = 16y2 - 36x2
AB + CD = 25y2 - 100x2
AB + CD = 25(y2 - 4x2)
AB + CD = 25(y + 2x)(y - 2x)

now given AB + CD = -275
hence
-275= 25(y + 2x)(y - 2x)
-11=(y + 2x)(y - 2x)
now
(y + 2x)=-11 or (y - 2x)=-11
Y=+1,X=-6 OR Y=1,X=5
INSUFFICIENT

option2
AD = (3y + 8x)(4y - 6x) = 12y2 + 14xy - 48x2
BC = (3y - 8x)(4y + 6x) = 12y2 - 14xy - 48x2
AD - BC = 14xy - (-14xy) = 28xy

given AD - BC = 420
hence
420=28xy
xy=15
suff
mehulv wrote:Given that A = 3y + 8x, B = 3y - 8x, C = 4y + 6x, and D = 4y - 6x, what is the value of x*y?

1. AB + CD = -275
2. AD - BC = 420
-------------------------------------
--------------------------------------
General blog
https://amarnaik.wordpress.com
MBA blog
https://amarrnaik.blocked/
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1