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

Redeem

DS-Maths

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
User avatar
Master | Next Rank: 500 Posts
Posts: 324
Joined: Mon Jul 05, 2010 6:44 am
Location: London
Thanked: 70 times
Followed by:3 members

by kmittal82 » Tue Oct 26, 2010 5:51 am
1 is clearly not enough on its own

2)

Sq both sides

x^3 - 9x + 4 > 4

x(x^2 - 9) > 0

x(x-3)(x+3) > 0

the above holds true for all x>3, and but also for say x = -1, so not sufficient

Combining 1 and 2, we know that x > 0, and for x(x-3)(x+3) > 0 to hold true with that precondition, x must be greater than 3

hence (C)

OA please?
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pm
Location: Milpitas, CA
Thanked: 447 times
Followed by:88 members

by Rahul@gurome » Tue Oct 26, 2010 5:55 am
sanyalpritish wrote:If x>3?

a)x>0
b)Sq root(x^3-9x+4)>2
I think the question should be Is x > 3?
In that case,

Statement 1: x > 0 => x may or may not be grater than 3.

Not sufficient.

Statement 2: sqrt(x^3 - 9x + 4) > 2 => (x^3 - 9x + 4) > 4 => (x^3 - 9x) > 0 => x(x + 3)(x - 3) > 0
Implies, either -3 < x < 0 or x > 3

Not sufficient.


1 & 2 Together: x > 3

Both statements together are sufficient.
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 106
Joined: Tue Mar 23, 2010 8:04 pm
Thanked: 2 times

by sanyalpritish » Tue Oct 26, 2010 6:10 am
When U take option B

we get
1. x>0
2.x>-3
3.x>3

Now as Option A gives x>0 hence x>-3 is eliminated.

But combing still does not tell us that x>3 because Option a and b give us just that x>0

So how come option C is the answer
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pm
Location: Milpitas, CA
Thanked: 447 times
Followed by:88 members

by Rahul@gurome » Tue Oct 26, 2010 6:20 am
sanyalpritish wrote:When U take option B

we get
1. x>0
2.x>-3
3.x>3

Now as Option A gives x>0 hence x>-3 is eliminated.

But combing still does not tell us that x>3 because Option a and b give us just that x>0

So how come option C is the answer
When we take statement B, we get either -3 < x < 0 or x > 3. To understand this consider the following (try putting some values like -4, -1, 2, 5 etc),
1. x(x + 3)(x - 3) < 0 for x < -3
2. x(x + 3)(x - 3) > 0 for -3 < x <0
3. x(x + 3)(x - 3) < 0 for 0 < x < 3
4. x(x + 3)(x - 3) > 0 for x > 3
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Post new topic Post Reply
• Page 1 of 1