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

 It is currently 17 Jun 2018, 21:10

### 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

# Is ab positive?

Author Message
TAGS:

### Hide Tags

Manager
Joined: 15 Mar 2014
Posts: 140
Location: India
Concentration: Technology, General Management
GPA: 3.5
WE: Operations (Telecommunications)

### Show Tags

08 Mar 2017, 06:04
1
00:00

Difficulty:

35% (medium)

Question Stats:

54% (00:36) correct 46% (00:42) wrong based on 41 sessions

### HideShow timer Statistics

Is ab positive?

1. $$(a + b)^{2} < (a - b)^{2}$$
2. a = b

_________________

Hit +1 Kudos If you like my post!

Math Expert
Joined: 02 Sep 2009
Posts: 46047

### Show Tags

08 Mar 2017, 06:15
Is ab positive?

(1) $$(a + b)^{2}$$ < $$(a - b)^{2}$$

$$a^2 + 2ab + b^2 < a^2 - 2ab + b^2$$

$$4ab < 0$$

$$ab<0$$

Sufficient.

(2) a = b. If a = b = 0, then ab = 0 but if a = b = 1, then ab = 1 > 0. Not sufficient.

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 46047

### Show Tags

08 Mar 2017, 06:29
1
Bunuel wrote:
Is ab positive?

(1) $$(a + b)^{2}$$ < $$(a - b)^{2}$$

$$a^2 + 2ab + b^2 < a^2 - 2ab + b^2$$

$$4ab < 0$$

$$ab<0$$

Sufficient.

(2) a = b. If a = b = 0, then ab = 0 but if a = b = 1, then ab = 1 > 0. Not sufficient.

Just noticed - statements contradict here. ab<0 and a=b cannot simultaneously be true. So, the question is flawed: On the GMAT, two data sufficiency statements always provide TRUE information and these statements NEVER contradict each other or the stem.

Are you sure you copied the question correctly?
_________________
SVP
Joined: 26 Mar 2013
Posts: 1671

### Show Tags

09 Mar 2017, 03:21
ashwink wrote:
Is ab positive?

1. $$(a + b)^{2} < (a - b)^{2}$$
2. a = b

Can you please specify from which test you copied the question above? I have searched in all 9 GMAC paper tests and did not find this question. Maybe I missed something.

Thanks
Manager
Joined: 14 Oct 2015
Posts: 243
GPA: 3.57

### Show Tags

09 Mar 2017, 04:17
Bunuel wrote:
Is ab positive?

(1) $$(a + b)^{2}$$ < $$(a - b)^{2}$$

$$a^2 + 2ab + b^2 < a^2 - 2ab + b^2$$

$$4ab < 0$$

$$ab<0$$

Sufficient.

(2) a = b. If a = b = 0, then ab = 0 but if a = b = 1, then ab = 1 > 0. Not sufficient.

Am I correct in my assertion that you cannot assume 0 as positive and hence second statement becomes insufficient?
_________________

Please hit Kudos if this post helped you inch closer to your GMAT goal.
Procrastination is the termite constantly trying to eat your GMAT tree from the inside.
There is one fix to every problem, working harder!

Manager
Joined: 15 Mar 2014
Posts: 140
Location: India
Concentration: Technology, General Management
GPA: 3.5
WE: Operations (Telecommunications)

### Show Tags

09 Mar 2017, 06:32
Bunuel wrote:
Bunuel wrote:
Is ab positive?

(1) $$(a + b)^{2}$$ < $$(a - b)^{2}$$

$$a^2 + 2ab + b^2 < a^2 - 2ab + b^2$$

$$4ab < 0$$

$$ab<0$$

Sufficient.

(2) a = b. If a = b = 0, then ab = 0 but if a = b = 1, then ab = 1 > 0. Not sufficient.

Just noticed - statements contradict here. ab<0 and a=b cannot simultaneously be true. So, the question is flawed: On the GMAT, two data sufficiency statements always provide TRUE information and these statements NEVER contradict each other or the stem.

Are you sure you copied the question correctly?

Looks like I copied the question from a wrong source. Apologies. Please remove the thread if this is a poor quality question.

Could you please however explain how the contradiction happened? We do have a clear YES in statement 1 & and multiple choice(YES and a NO) in statement 2 making it insufficient.
As per the source(practice question from another material), the OA is A as per this explanation. Why are we trying to combine statement 1 & 2 when we have a definite YES in 1?
_________________

Hit +1 Kudos If you like my post!

Math Expert
Joined: 02 Sep 2009
Posts: 46047

### Show Tags

09 Mar 2017, 06:54
ashwink wrote:
Bunuel wrote:
Bunuel wrote:
Is ab positive?

(1) $$(a + b)^{2}$$ < $$(a - b)^{2}$$

$$a^2 + 2ab + b^2 < a^2 - 2ab + b^2$$

$$4ab < 0$$

$$ab<0$$

Sufficient.

(2) a = b. If a = b = 0, then ab = 0 but if a = b = 1, then ab = 1 > 0. Not sufficient.

Just noticed - statements contradict here. ab<0 and a=b cannot simultaneously be true. So, the question is flawed: On the GMAT, two data sufficiency statements always provide TRUE information and these statements NEVER contradict each other or the stem.

Are you sure you copied the question correctly?

Looks like I copied the question from a wrong source. Apologies. Please remove the thread if this is a poor quality question.

Could you please however explain how the contradiction happened? We do have a clear YES in statement 1 & and multiple choice(YES and a NO) in statement 2 making it insufficient.
As per the source(practice question from another material), the OA is A as per this explanation. Why are we trying to combine statement 1 & 2 when we have a definite YES in 1?

(1) says that ab < 0, so a and b have different signs, which in tiurn means that a does not equal to b.
(2) says that a = b

The statements clearly contradict each other.
_________________
Board of Directors
Joined: 17 Jul 2014
Posts: 2730
Location: United States (IL)
Concentration: Finance, Economics
GMAT 1: 650 Q49 V30
GPA: 3.92
WE: General Management (Transportation)

### Show Tags

09 Mar 2017, 08:52
A for me too. Arrived at the solution the same way as Bunuel did.
what is the difficulty level of this question?
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 2738
Location: United States (CA)

### Show Tags

15 Mar 2017, 16:24
ashwink wrote:
Is ab positive?

1. $$(a + b)^{2} < (a - b)^{2}$$
2. a = b

We need to determine whether ab > 0.

Statement One Alone:

(a + b)^2 < (a - b)^2

We can simplify the information in statement one:

(a + b)^2 < (a - b)^2

a^2 + 2ab + b^2 < a^2 - 2ab + b^2

2ab < -2ab

4ab < 0

ab < 0

Since ab is less than zero, ab is not positive. Statement one is sufficient to answer the question.

Statement Two Alone:

a = b

The information in statement two is not sufficient to answer the question. If a and b are both 1, then ab is positive; however, if a and b are both 0, then ab is NOT positive.

_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Re: Is ab positive?   [#permalink] 15 Mar 2017, 16:24
Display posts from previous: Sort by