It is currently 22 Mar 2018, 18:30

### 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

# PS: Always negative?

Author Message
Retired Moderator
Joined: 18 Jul 2008
Posts: 920

### Show Tags

02 Mar 2009, 15:33
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

### HideShow timer Statistics

If |A| < |B| , which of the following numbers is always negative?

a) A/B - B/A

b) A-B/A+B

c) (A^B)-(B^A)

d) A (B/A-B)

e) B-A/B

Is there a fast way of solving these, other than plugging and chugging numbers?

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
SVP
Joined: 29 Aug 2007
Posts: 2453

### Show Tags

08 Mar 2009, 14:19
If |A| < |B| , which of the following numbers is always negative?

a) A/B - B/A
b) A-B/A+B
c) (A^B)-(B^A)
d) A (B/A-B)
e) B-A/B

Is there a fast way of solving these, other than plugging and chugging numbers?

I use POE not plugging-in nor chugging-in.

Given that: |A| < |B|

The clue: which of the following is always -ve?
So lets try finding +ve one.

a) A/B - B/A: If A and B both are -ve, the expression is +ve. out.
b) (A-B)/(A+B): It is in any case -ve...
c) (A^B)-(B^A): If A is -ve integer, and B is +ve integer, the expression is +ve. out.
d) A (B/(A-B)): If A and B both are -ve, the expression is +ve. out.
e) B - (A/B): If A is -ve (or even +ve) and B is +ve, the expression is +ve. out.

So B.
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Retired Moderator
Joined: 18 Jul 2008
Posts: 920

### Show Tags

09 Mar 2009, 13:48
I really don't understand this part:

Given that: |A| < |B|
The clue: which of the following is always -ve?
So lets try finding +ve one.

GMAT TIGER wrote:
If |A| < |B| , which of the following numbers is always negative?

a) A/B - B/A
b) A-B/A+B
c) (A^B)-(B^A)
d) A (B/A-B)
e) B-A/B

Is there a fast way of solving these, other than plugging and chugging numbers?

I use POE not plugging-in nor chugging-in.

Given that: |A| < |B|

The clue: which of the following is always -ve?
So lets try finding +ve one.

a) A/B - B/A: If A and B both are -ve, the expression is +ve. out.
b) (A-B)/(A+B): It is in any case -ve...
c) (A^B)-(B^A): If A is -ve integer, and B is +ve integer, the expression is +ve. out.
d) A (B/(A-B)): If A and B both are -ve, the expression is +ve. out.
e) B - (A/B): If A is -ve (or even +ve) and B is +ve, the expression is +ve. out.

So B.
SVP
Joined: 07 Nov 2007
Posts: 1760
Location: New York

### Show Tags

11 Mar 2009, 22:22
If |A| < |B| , which of the following numbers is always negative?

a) A/B - B/A

b) A-B/A+B

c) (A^B)-(B^A)

d) A (B/A-B)

e) B-A/B

Is there a fast way of solving these, other than plugging and chugging numbers?

A-B/A+B

= {(A/B)-1 } / {(A/B)+1}

|A| < |B| --> means magnitude of A/B <1

A/B lies between -1 and 1
i.e -1<A/B<1

= {(A/B)-1 } / {(A/B)+1}

clearly neumarotr -ve for that range
denominator +ve for that range.. it (B) is always negative.

B
_________________

Smiling wins more friends than frowning

Director
Joined: 01 Apr 2008
Posts: 846
Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014

### Show Tags

14 Mar 2009, 01:54
Hi GmatTiger,

I could not understand: a) A/B - B/A: If A and B both are -ve, the expression is +ve. out.

if A and B are both -ve, A/B is +ve, and B/A is +ve. Now,
A/B - B/A should be -ve because...magnitude of A is less than B, which means A/B < B/A !!

Similarly,
c) (A^B)-(B^A): If A is -ve integer, and B is +ve integer, the expression is +ve. out.

Here, A^B can be -ve or +ve depending upon B is odd or even,
B^A will be 1/B^A (as A is -ve) , How can u conclude that the expression is +ve ??

GMAT TIGER wrote:
If |A| < |B| , which of the following numbers is always negative?

a) A/B - B/A
b) A-B/A+B
c) (A^B)-(B^A)
d) A (B/A-B)
e) B-A/B

Is there a fast way of solving these, other than plugging and chugging numbers?

I use POE not plugging-in nor chugging-in.

Given that: |A| < |B|

The clue: which of the following is always -ve?
So lets try finding +ve one.

a) A/B - B/A: If A and B both are -ve, the expression is +ve. out.
b) (A-B)/(A+B): It is in any case -ve...
c) (A^B)-(B^A): If A is -ve integer, and B is +ve integer, the expression is +ve. out.
d) A (B/(A-B)): If A and B both are -ve, the expression is +ve. out.
e) B - (A/B): If A is -ve (or even +ve) and B is +ve, the expression is +ve. out.

So B.
SVP
Joined: 29 Aug 2007
Posts: 2453

### Show Tags

15 Mar 2009, 06:56
That is because if we find all possible +ves, we can rule out those +ves so that the remaining is -ve.
I really don't understand this part:

Given that: |A| < |B|
The clue: which of the following is always -ve?
So lets try finding +ve one.

_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

SVP
Joined: 29 Aug 2007
Posts: 2453

### Show Tags

15 Mar 2009, 08:07
Thanks for pointing out that A and C are not complete in my previous posts. I thought correctly but wrote incorrectly. A has typo but C should be revised.

Economist wrote:
Hi GmatTiger,

I could not understand: a) A/B - B/A: If A and B both are -ve, the expression is +ve. out.

if A and B are both -ve, A/B is +ve, and B/A is +ve. Now,
A/B - B/A should be -ve because...magnitude of A is less than B, which means A/B < B/A !!

Similarly,
c) (A^B)-(B^A): If A is -ve integer, and B is +ve integer, the expression is +ve. out.

Here, A^B can be -ve or +ve depending upon B is odd or even,
B^A will be 1/B^A (as A is -ve) , How can u conclude that the expression is +ve ??

If |A| < |B| , which of the following numbers is always negative?

a) A/B - B/A
b) A-B/A+B
c) (A^B)-(B^A)
d) A (B/A-B)
e) B-A/B

Is there a fast way of solving these, other than plugging and chugging numbers?

Given that: |A| < |B|

The clue: which of the following is always -ve?
So lets try finding +ve one.

a) A/B - B/A: If one is +ve and the other is -ve, the expression is +ve. out.
b) (A-B)/(A+B): It is in any case -ve...
c) (A^B)-(B^A): If A is +ve odd integer, and B is -ve integer, the expression is +ve. out.

For ex: A = 3 and B = -4:
(A^B)-(B^A) = 3^(-4) - (-4)^3 = 1/81 - (-256) = 256 approx.

d) A (B/(A-B)): If A and B both are -ve, the expression is +ve. out.
e) B - (A/B): If A is -ve (or even +ve) and B is +ve, the expression is +ve. out.

So B.
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Manager
Joined: 02 Mar 2009
Posts: 129

### Show Tags

15 Mar 2009, 08:32
I think the quickest and safest way is by plugging in numbers:

Consider 4 possibilities for each of them:

A=-1, B=-5
A=1, B=5
A=-1, B=5
A=1, B=-5

Just plug them in for each of them and you will find B gives a negative answer for each of the cases.

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: PS: Always negative?   [#permalink] 15 Mar 2009, 08:32
Display posts from previous: Sort by