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 →

MGMAT CAT 2: PS Problem

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Sun Nov 10, 2013 10:42 am
josh80 wrote:Which of the following points could lie in the same quadrant of the xy-coordinate plane as the point (a, b), where ab ≠ 0 ?

(-b, -a)

(-a, -b)

(b, -a)

(a, -b)

(-b, a)
Every answer choice includes at least one negative sign.
Test coordinate pairs that include at least one negative value.

Case 1: a=1 and b=-1, so that (a, b) = (1, -1)
Plug a=1 and b=-1 into the answer choices to see whether one of the answer choices yields a point in the same quadrant as (1,-1).

A: (-b, -a) = ( -(-1), -1 ) = (1, -1).
Success!

The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members
Location: Palo Alto, CA
Thanked: 2867 times
GMAT Score:800

by [email protected] » Sun Nov 10, 2013 12:44 pm
Hi josh80,

Co-ordinate Geometry (or "graphing", as most people call it) is a relatively small category in the GMAT Quant section; you'll likely see just 1 of these questions on Test Day. The question is perfect for TESTing Values. Here's how:

We're asked which of the 5 answers COULD be in the same quadrant as (a,b), where neither a nor b equals 0. This makes me think that we'll have to consider more than one possibility, since there are 4 different quadrants on a graph.

Here are the examples that I would consider:
(a,b)
(1,2) - Quadrant 1
(-1,2) - Quadrant 2
(-1,-2) - Quadrant 3
(1,-2) - Quadrant 4

You'll notice that each of the 5 answer choices changes the "sign" of at least one of the variables (and sometimes switches the variables around). If you start off in Quadrant 1, the only way to end up in that SAME Quadrant is if both the a and b are positive. That doesn't happen in ANY of the answer choices, so we need to look at a diffent Quadrant. I'm going to start with:

Quadrant 2:
(a,b)
(-1,2)

So, if we plug a = -1 and b = 2 into the 5 answer choices, do any of them give us an answer that puts us in Quadrant 2?

[spoiler]Answer A: (-b,-a) = (-2,1). [/spoiler] THAT answer puts in Quadrant 2. It's a match for what the question asked us for, so it has to be the answer.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 447
Joined: Fri Nov 08, 2013 7:25 amFollowed by: 1 member
Thanked: 25 times

by Mathsbuddy » Sun Nov 17, 2013 9:26 am
(a,b) options: (+,-), (-,+), (+,+), (-,-).
Substituting into each answer gives:
(A) (-b, -a) : (+,-), (-,+), (-,-), (+,+)
(B) (-a, -b) : (-,+), (+,-), (-,-), (+,+)
(C) (b, -a) : (-,-), (+,+), (+,-), (-,+)
(D) (a, -b) : (+,+), (-,-), (+,-), (-,+)
(E) (-b, a) : (+,+), (-,-), (-,+), (+,-)

The colours above indicate that only answer A satisfies the condition.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 447
Joined: Fri Nov 08, 2013 7:25 amFollowed by: 1 member
Thanked: 25 times

by Mathsbuddy » Sun Nov 17, 2013 9:38 am
Another approach:

x can never equal -x
y can never equal -y

so we can instantly eliminate B and D.

x and y must share the same sign,

so we can also eliminate C and E

This leaves answer A in only a matter of seconds, without any substitution required.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1