GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 19 Oct 2018, 00:58

### 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

# If ab > 0, is ab^2 > 0 ?

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6386
GMAT 1: 760 Q51 V42
GPA: 3.82
If ab > 0, is ab^2 > 0 ?  [#permalink]

### Show Tags

16 Oct 2017, 01:55
1
00:00

Difficulty:

45% (medium)

Question Stats:

64% (00:55) correct 36% (00:44) wrong based on 61 sessions

### HideShow timer Statistics

[GMAT math practice question]

If ab > 0, is ab^2 > 0 ?

1) a > 0
2) b > 0

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only \$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Senior Manager
Joined: 17 Oct 2016
Posts: 322
Location: India
Concentration: Operations, Strategy
GPA: 3.73
WE: Design (Real Estate)
Re: If ab > 0, is ab^2 > 0 ?  [#permalink]

### Show Tags

16 Oct 2017, 02:32
From Q stem we can conclude both a and b can be positive or both can be negative.

From st1 we can conclude a is positive. Hence b is also positive. So the square of the product will be positive

St2 also says same as above. Hence the square of the product will be positive.
Hence D

Posted from my mobile device
_________________

Help with kudos if u found the post useful. Thanks

Manager
Joined: 07 Jun 2017
Posts: 174
Location: India
Concentration: Technology, General Management
GMAT 1: 660 Q46 V38
GPA: 3.6
WE: Information Technology (Computer Software)
Re: If ab > 0, is ab^2 > 0 ?  [#permalink]

### Show Tags

16 Oct 2017, 03:17
Given ab > 0
So a and b both should be same sign.

1. a>0 so b should be greater than 0 so ab^2 should be grater than 0. Sufficient
2. b>0 so a should be greater than 0 so ab^2 should be grater than 0. Sufficient.

_________________

Regards,
Naveen
email: nkmungila@gmail.com
Please press kudos if you like this post

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6386
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: If ab > 0, is ab^2 > 0 ?  [#permalink]

### Show Tags

18 Oct 2017, 03:13
=>

Forget conventional ways of solving math questions. In DS, VA (Variable Approach) method is the easiest and quickest way to find the answer without actually solving the problem. Remember that equal number of variables and independent equations ensures a solution.

The first step of VA(Variable Approach) method is modifying the original condition and the question, and rechecking the number of variables and the number of equations.

Under the condition ab > 0, the question ab2 > 0 is equivalent to a > 0.

The condition 1) is equivalent to the question a > 0. This is sufficient.
And under the original condition ab > 0, the condition 2) b > 0 is equivalent to a > 0. This is sufficient too.

By the tip 1) of VA method, since two conditions are same, we can choose D as the answer.

Ans: D
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only \$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Re: If ab > 0, is ab^2 > 0 ? &nbs [#permalink] 18 Oct 2017, 03:13
Display posts from previous: Sort by