• Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • 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
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • 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
  • 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
  • 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
  • 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

DS weakness - Inequalities - advise- taking GMAT this week

This topic has 1 expert reply and 5 member replies
swati.arunahuja Junior | Next Rank: 30 Posts Default Avatar
Joined
15 Jul 2008
Posted:
12 messages

DS weakness - Inequalities - advise- taking GMAT this week

Post Mon Jul 21, 2008 12:09 am
Hi,

I'm particularly weak in the DS questions pertaining to Inequalities. Would any have any last minute piece of advise for me?
Also, I'm taking the test dayafter, so your last minute advise is most welcome:)
Thanks in advance

Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!

GMAT/MBA Expert

lunarpower GMAT Instructor
Joined
03 Mar 2008
Posted:
3380 messages
Followed by:
1474 members
Thanked:
2255 times
GMAT Score:
800
Post Mon Jul 21, 2008 1:11 am
swati.arunahuja wrote:
Hi,

I'm particularly weak in the DS questions pertaining to Inequalities. Would any have any last minute piece of advise for me?
Also, I'm taking the test dayafter, so your last minute advise is most welcome:)
Thanks in advance
there are only a couple of things you really have to know about inequalities, but the number of ways in which those things are combined is almost endless.

here are the facts you need to know:

* when you have SIMULTANEOUS INEQUALITIES, here's the simplest guideline to follow:
- ADD only
- MAKE SURE THE INEQUALITY SIGNS FACE THE SAME WAY

for instance, if you are given the inequalities z - 3m > 0 and 4m - z > 0, you can add those in their current state (since both of the inequality signs are "greater than") to yield m > 0.

if you are given, say, a < b and c > d, and you wanted to combine them, you'd simply turn one of them around by multiplying by a negative quantity, usually -1:
-a > -b
c > d
add: c - a > d - b
there are rules you could memorize for subtracting inequalities, but they're a pain - you have to make sure the inequality signs are facing opposite ways, and, worse yet, you have to know which way the sign is supposed to face after you perform the subtraction. that is not friendly - and it produces the same result as multiplying one side by -1 and then adding anyway.

* do not ever forget to FLIP THE INEQUALITY SIGN when you MULTIPLY OR DIVIDE BY A NEGATIVE NUMBER.
also, corollary: if you DON'T KNOW THE SIGN OF A VARIABLE in an inequality, YOU CAN'T DIVIDE OR MULTIPLY BY IT.
this means that you can't "cross multiply" most inequalities, because cross multiplying is really multiplying by both denominators.
see http://www.manhattangmat.com/forums/if-x-does-not-equal-y-t2997.html for a problem of this type, on which i made copious comments about what you can and can't do with inequalities (sorry for the cross posting).

_________________
Ron has been teaching various standardized tests for 20 years.

--

Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

--

Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.

Yves Saint-Laurent

--

Learn more about ron

Thanked by: JDesai01, Alokgoolya, chendawg
Free Manhattan Prep online events - The first class of every online Manhattan Prep course is free. Classes start every week.
swati.arunahuja Junior | Next Rank: 30 Posts Default Avatar
Joined
15 Jul 2008
Posted:
12 messages
Post Mon Jul 21, 2008 7:10 pm
lunarpower wrote:
swati.arunahuja wrote:
Hi,

I'm particularly weak in the DS questions pertaining to Inequalities. Would any have any last minute piece of advise for me?
Also, I'm taking the test dayafter, so your last minute advise is most welcome:)
Thanks in advance
there are only a couple of things you really have to know about inequalities, but the number of ways in which those things are combined is almost endless.

here are the facts you need to know:

* when you have SIMULTANEOUS INEQUALITIES, here's the simplest guideline to follow:
- ADD only
- MAKE SURE THE INEQUALITY SIGNS FACE THE SAME WAY

for instance, if you are given the inequalities z - 3m > 0 and 4m - z > 0, you can add those in their current state (since both of the inequality signs are "greater than") to yield m > 0.

if you are given, say, a < b and c > d, and you wanted to combine them, you'd simply turn one of them around by multiplying by a negative quantity, usually -1:
-a > -b
c > d
add: c - a > d - b
there are rules you could memorize for subtracting inequalities, but they're a pain - you have to make sure the inequality signs are facing opposite ways, and, worse yet, you have to know which way the sign is supposed to face after you perform the subtraction. that is not friendly - and it produces the same result as multiplying one side by -1 and then adding anyway.

* do not ever forget to FLIP THE INEQUALITY SIGN when you MULTIPLY OR DIVIDE BY A NEGATIVE NUMBER.
also, corollary: if you DON'T KNOW THE SIGN OF A VARIABLE in an inequality, YOU CAN'T DIVIDE OR MULTIPLY BY IT.
this means that you can't "cross multiply" most inequalities, because cross multiplying is really multiplying by both denominators.
see http://www.manhattangmat.com/forums/if-x-does-not-equal-y-t2997.html for a problem of this type, on which i made copious comments about what you can and can't do with inequalities (sorry for the cross posting).
Thanks a lot Ron

swati.arunahuja Junior | Next Rank: 30 Posts Default Avatar
Joined
15 Jul 2008
Posted:
12 messages
Post Mon Jul 21, 2008 7:11 pm
lunarpower wrote:
swati.arunahuja wrote:
Hi,

I'm particularly weak in the DS questions pertaining to Inequalities. Would any have any last minute piece of advise for me?
Also, I'm taking the test dayafter, so your last minute advise is most welcome:)
Thanks in advance
there are only a couple of things you really have to know about inequalities, but the number of ways in which those things are combined is almost endless.

here are the facts you need to know:

* when you have SIMULTANEOUS INEQUALITIES, here's the simplest guideline to follow:
- ADD only
- MAKE SURE THE INEQUALITY SIGNS FACE THE SAME WAY

for instance, if you are given the inequalities z - 3m > 0 and 4m - z > 0, you can add those in their current state (since both of the inequality signs are "greater than") to yield m > 0.

if you are given, say, a < b and c > d, and you wanted to combine them, you'd simply turn one of them around by multiplying by a negative quantity, usually -1:
-a > -b
c > d
add: c - a > d - b
there are rules you could memorize for subtracting inequalities, but they're a pain - you have to make sure the inequality signs are facing opposite ways, and, worse yet, you have to know which way the sign is supposed to face after you perform the subtraction. that is not friendly - and it produces the same result as multiplying one side by -1 and then adding anyway.

* do not ever forget to FLIP THE INEQUALITY SIGN when you MULTIPLY OR DIVIDE BY A NEGATIVE NUMBER.
also, corollary: if you DON'T KNOW THE SIGN OF A VARIABLE in an inequality, YOU CAN'T DIVIDE OR MULTIPLY BY IT.
this means that you can't "cross multiply" most inequalities, because cross multiplying is really multiplying by both denominators.
see http://www.manhattangmat.com/forums/if-x-does-not-equal-y-t2997.html for a problem of this type, on which i made copious comments about what you can and can't do with inequalities (sorry for the cross posting).
Thanks a lot Ron

swati.arunahuja Junior | Next Rank: 30 Posts Default Avatar
Joined
15 Jul 2008
Posted:
12 messages
Post Mon Jul 21, 2008 7:18 pm
lunarpower wrote:
swati.arunahuja wrote:
Hi,

I'm particularly weak in the DS questions pertaining to Inequalities. Would any have any last minute piece of advise for me?
Also, I'm taking the test dayafter, so your last minute advise is most welcome:)
Thanks in advance
there are only a couple of things you really have to know about inequalities, but the number of ways in which those things are combined is almost endless.

here are the facts you need to know:

* when you have SIMULTANEOUS INEQUALITIES, here's the simplest guideline to follow:
- ADD only
- MAKE SURE THE INEQUALITY SIGNS FACE THE SAME WAY

for instance, if you are given the inequalities z - 3m > 0 and 4m - z > 0, you can add those in their current state (since both of the inequality signs are "greater than") to yield m > 0.

if you are given, say, a < b and c > d, and you wanted to combine them, you'd simply turn one of them around by multiplying by a negative quantity, usually -1:
-a > -b
c > d
add: c - a > d - b
there are rules you could memorize for subtracting inequalities, but they're a pain - you have to make sure the inequality signs are facing opposite ways, and, worse yet, you have to know which way the sign is supposed to face after you perform the subtraction. that is not friendly - and it produces the same result as multiplying one side by -1 and then adding anyway.

* do not ever forget to FLIP THE INEQUALITY SIGN when you MULTIPLY OR DIVIDE BY A NEGATIVE NUMBER.
also, corollary: if you DON'T KNOW THE SIGN OF A VARIABLE in an inequality, YOU CAN'T DIVIDE OR MULTIPLY BY IT.
this means that you can't "cross multiply" most inequalities, because cross multiplying is really multiplying by both denominators.
see http://www.manhattangmat.com/forums/if-x-does-not-equal-y-t2997.html for a problem of this type, on which i made copious comments about what you can and can't do with inequalities (sorry for the cross posting).
Thanks a lot Ron

JDesai01 Junior | Next Rank: 30 Posts Default Avatar
Joined
04 Jul 2008
Posted:
22 messages
Post Tue Jul 22, 2008 7:04 pm
lunarpower- this was a enormously helpful post. Do you have other helpful thoughts like this aggregated somewhere? Seriously, thanks a ton, this has really helped how I approach inequality questions.

And thanks to whoever asked the question!

sumithshah Master | Next Rank: 500 Posts Default Avatar
Joined
28 May 2008
Posted:
165 messages
Thanked:
9 times
Test Date:
11/14/2008
Target GMAT Score:
700+
GMAT Score:
730
Post Thu Oct 23, 2008 10:03 pm
Ron

Can you throw some light on the rules of subtracting in equalities?

Best Conversation Starters

1 LUANDATO 157 topics
2 lheiannie07 87 topics
3 Roland2rule 75 topics
4 ardz24 64 topics
5 AAPL 58 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 image description EconomistGMATTutor

The Economist GMAT Tutor

163 posts
2 image description GMATGuruNY

The Princeton Review Teacher

133 posts
3 image description Jay@ManhattanReview

Manhattan Review

128 posts
4 image description Rich.C@EMPOWERgma...

EMPOWERgmat

121 posts
5 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

100 posts
See More Top Beat The GMAT Experts