It is currently 19 Oct 2017, 04:31

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# multiplying by unknown variables in inequalities

Author Message
TAGS:

### Hide Tags

Manager
Joined: 08 Sep 2010
Posts: 56

Kudos [?]: 34 [0], given: 4

multiplying by unknown variables in inequalities [#permalink]

### Show Tags

06 Oct 2011, 11:36
In the MGMAT book, it mentions that when multiplying by unknown variables, take both positive/negative scenarios into account

4/x<1/3?

1. 12<x

2. little confused here. do I take x to be -x?
4/-x<1/3
12<-x
-12>x?

?????
_________________

Don't forget to give me ****KUDOS****

Kudos [?]: 34 [0], given: 4

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7674

Kudos [?]: 17357 [1], given: 232

Location: Pune, India
Re: multiplying by unknown variables in inequalities [#permalink]

### Show Tags

07 Oct 2011, 03:34
1
KUDOS
Expert's post
386390 wrote:
In the MGMAT book, it mentions that when multiplying by unknown variables, take both positive/negative scenarios into account

4/x<1/3?

1. 12<x

2. little confused here. do I take x to be -x?
4/-x<1/3
12<-x
-12>x?

?????

Best way to deal with inequalities is by keeping 0 on the right hand side.

Is 4/x < 1/3?
Is 4/x - 1/3 < 0?
Is (12 - x)/3x < 0?
Is (x - 12)/3x > 0

When will (x-12)/3x be positive?

It will be positive when x > 12 or when x < 0 (How? You can find it in a moment. Check out this thread: inequalities-trick-91482.html?hilit=trick%20inequalities )

Statement 1 is sufficient.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for \$199

Veritas Prep Reviews

Kudos [?]: 17357 [1], given: 232

Manager
Joined: 21 Aug 2010
Posts: 186

Kudos [?]: 128 [0], given: 141

Location: United States
GMAT 1: 700 Q49 V35
Re: multiplying by unknown variables in inequalities [#permalink]

### Show Tags

06 Oct 2011, 13:50
Its not the value of x you need to put as negative.

When you substitute a sample value in an equation you need to check with both positive an negative values

for ur question

4/x<1/3?

1. 12<x

if above is the statement 1 then no need to substitute a negative value as they have given x>12

means take some number more than 12 (take 13)

then eqn will become

4/13<1/3
==>12/39<13/39 then given eqn is correct

1 is sufficient
_________________

-------------------------------------

Kudos [?]: 128 [0], given: 141

Manager
Joined: 21 Aug 2010
Posts: 186

Kudos [?]: 128 [0], given: 141

Location: United States
GMAT 1: 700 Q49 V35
Re: multiplying by unknown variables in inequalities [#permalink]

### Show Tags

06 Oct 2011, 13:54
For the below question

inequality-121619.html

i tried to substitute x = -x and the method was confusing but when i assumed x as 2 and -2 it was easy to identify whether the statement is enough or not
_________________

-------------------------------------

Kudos [?]: 128 [0], given: 141

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16678

Kudos [?]: 273 [0], given: 0

Re: multiplying by unknown variables in inequalities [#permalink]

### Show Tags

01 Nov 2014, 23:32
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

Re: multiplying by unknown variables in inequalities   [#permalink] 01 Nov 2014, 23:32
Display posts from previous: Sort by