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

 It is currently 20 Oct 2019, 02:33

### 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 pq = -8, what is the value of pq(p - q) ?

Author Message
TAGS:

### Hide Tags

Manager
Joined: 04 May 2009
Posts: 113
Location: London
Schools: Haas (WL), Kellogg (matricultating), Stanford (R2, ding), Columbia (ding)
WE 1: 3 years hotel industry sales and marketing France
WE 2: 3 years financial industry marketing UK
If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

17 May 2010, 12:53
7
00:00

Difficulty:

85% (hard)

Question Stats:

50% (02:21) correct 50% (02:13) wrong based on 114 sessions

### HideShow timer Statistics

If pq = -8, what is the value of pq(p - q) ?

(1) p + q = 7
(2) pq^2 = -64

_________________
Yes I can!
Manager
Joined: 24 Jul 2009
Posts: 208
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

17 May 2010, 13:15
nifoui wrote:
DS question from Knewton's free CAT test

If pq = -8, what is the value of pq(p-q) ?
1. p + q = 7
2. pq² = -64

I do not agree with OA provided and would like to know your reasoning and OA.

Will share OA and OE later.

IMO B,

Statement 1:

Given pq=-1, so what can be the values of (p,q) >>> (1,-8),(2,-4),(-1,8),(-2,4),(4,-2),(-4,2),(-8,1),(8,-1)
Given p+q =7, it means >>> possible values are >>> (1,-8),(-1,8),(-8,1),(8,-1)

let say p=-1 and q=8
So pq(p-q) = -8(-1-8)= 72

Let say p= 1 and q= -8
So pq(p-q) = -8(1 + 8)= -72. Insufficient

Statement 2:

pq² = -64, also pq = -8...so
(pq)q =- 64
(-8)q =- 64
q= 8.....>>> So p can only be -1.
so pq(p-q) = -8(-1-8)= 72

OA plz.
Manager
Joined: 04 May 2009
Posts: 113
Location: London
Schools: Haas (WL), Kellogg (matricultating), Stanford (R2, ding), Columbia (ding)
WE 1: 3 years hotel industry sales and marketing France
WE 2: 3 years financial industry marketing UK
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

17 May 2010, 13:22
You are right OA is B, but I answered C and still hold my position.

Here is my reasoning:
From statement 2, there are multiple solutions:
p=-1 and q=8
or
p=-4 and q=4

Therefore statement 2 is not sufficient alone, but we can answer the question with both statements together.

Why is that wrong?
_________________
Yes I can!
Manager
Joined: 04 May 2009
Posts: 113
Location: London
Schools: Haas (WL), Kellogg (matricultating), Stanford (R2, ding), Columbia (ding)
WE 1: 3 years hotel industry sales and marketing France
WE 2: 3 years financial industry marketing UK
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

17 May 2010, 13:25
1

I had forgotten in the process that we were given pq = -8...

I'm loosing points with such mistakes!!

Thanks anyway
_________________
Yes I can!
Manager
Joined: 24 Jul 2009
Posts: 208
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

17 May 2010, 14:01
nifoui wrote:
You are right OA is B, but I answered C and still hold my position.

Here is my reasoning:
From statement 2, there are multiple solutions:
p=-1 and q=8
or
p=-4 and q=4

Therefore statement 2 is not sufficient alone, but we can answer the question with both statements together.

Why is that wrong?

Given in the question : p*q=-8
But if p=-4 and q=4 ..>>> Then p*q=-16
Intern
Joined: 21 Mar 2010
Posts: 12
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

17 May 2010, 15:03
If pq = -8, what is the value of pq(p-q) ?
1. p + q = 7
2. pq² = -64

1) Insufficient because it provides two values of pq(p-q) i.e. +72 and -72. If p+q and pq are known then we can derive square of p-q using the formula (p-q)^2 = (p+q)^2 -4pq. This formula gives p-q = +9 and -9.
So statement 1 doesn't provide unique value of pq(p-q).
2) Sufficient beacuse it provides p=8. and then plug p into pq will give q.

Board of Directors
Joined: 17 Jul 2014
Posts: 2509
Location: United States (IL)
Concentration: Finance, Economics
GMAT 1: 650 Q49 V30
GPA: 3.92
WE: General Management (Transportation)
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

08 Aug 2017, 15:22
nverma wrote:
nifoui wrote:
DS question from Knewton's free CAT test

If pq = -8, what is the value of pq(p-q) ?
1. p + q = 7
2. pq² = -64

I do not agree with OA provided and would like to know your reasoning and OA.

Will share OA and OE later.

IMO B,

Statement 1:

Given pq=-1, so what can be the values of (p,q) >>> (1,-8),(2,-4),(-1,8),(-2,4),(4,-2),(-4,2),(-8,1),(8,-1)
Given p+q =7, it means >>> possible values are >>> (1,-8),(-1,8),(-8,1),(8,-1)

let say p=-1 and q=8
So pq(p-q) = -8(-1-8)= 72

Let say p= 1 and q= -8
So pq(p-q) = -8(1 + 8)= -72. Insufficient

Statement 2:

pq² = -64, also pq = -8...so
(pq)q =- 64
(-8)q =- 64
q= 8.....>>> So p can only be -1.
so pq(p-q) = -8(-1-8)= 72

OA plz.

exactly my approach.

in statement 1, i ended up with q^2 + p^2 = 65. we can have different options here... so no way to find it...

statement2 - q=8, and p=-1. we can find the answer.

B
Intern
Joined: 06 Jul 2017
Posts: 7
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

08 Aug 2017, 17:46
nverma wrote:
nifoui wrote:
DS question from Knewton's free CAT test

If pq = -8, what is the value of pq(p-q) ?
1. p + q = 7
2. pq² = -64

I do not agree with OA provided and would like to know your reasoning and OA.

Will share OA and OE later.

IMO B,

Statement 1:

Given pq=-1, so what can be the values of (p,q) >>> (1,-8),(2,-4),(-1,8),(-2,4),(4,-2),(-4,2),(-8,1),(8,-1)
Given p+q =7, it means >>> possible values are >>> (1,-8),(-1,8),(-8,1),(8,-1)

let say p=-1 and q=8
So pq(p-q) = -8(-1-8)= 72

Let say p= 1 and q= -8
So pq(p-q) = -8(1 + 8)= -72. Insufficient

Statement 2:

pq² = -64, also pq = -8...so
(pq)q =- 64
(-8)q =- 64
q= 8.....>>> So p can only be -1.
so pq(p-q) = -8(-1-8)= 72

OA plz.
in statement 1, why did you assume that p,q are integers?

Sent from my iPhone using GMAT Club Forum mobile app
Manager
Joined: 07 Jun 2017
Posts: 100
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

08 Aug 2017, 20:07
pq^2 is confusing to me.
I thought it would be (pq)^2
but actually it is p*q*q,
now I know something

Posted from my mobile device
Director
Joined: 09 Mar 2018
Posts: 994
Location: India
Re: If pq = -8, what is the value of pq(p - q) ?  [#permalink]

### Show Tags

19 Feb 2019, 03:12
nifoui wrote:
If pq = -8, what is the value of pq(p - q) ?

(1) p + q = 7
(2) pq^2 = -64

From 1, we can get 2 values for p and q, such as p = -1 & q = 8 or p = 8 q =-1
Both will give different values

from 2, we will only get an unique value
p = -1 q = 8

B
_________________
If you notice any discrepancy in my reasoning, please let me know. Lets improve together.

Quote which i can relate to.
Many of life's failures happen with people who do not realize how close they were to success when they gave up.
Re: If pq = -8, what is the value of pq(p - q) ?   [#permalink] 19 Feb 2019, 03:12
Display posts from previous: Sort by