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

 It is currently 16 Oct 2019, 17:26 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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  Does (a – 2)(b + 4) = 8?

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

Hide Tags

Intern  S
Joined: 24 Nov 2018
Posts: 19
Location: India
Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

1
2 00:00

Difficulty:   45% (medium)

Question Stats: 60% (01:37) correct 40% (01:42) wrong based on 77 sessions

HideShow timer Statistics

Does (a – 2)(b + 4) = 8?

(1) ab = 2b – 4a
(2) a = 6

Source- Kaplan Mock Test
Manager  G
Joined: 11 Dec 2013
Posts: 121
Location: India
GMAT Date: 03-15-2015
WE: Education (Education)
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

1
(a – 2)(b + 4) = ab + 4a -2b - 8

(1) ab = 2b – 4a
ab+4a - 2b=0
Hence (a – 2)(b + 4) = ab + 4a -2b - 8 = 0 -8 = -8
Sufficient
(2) a = 6
(a – 2)(b + 4) = 4(b+4)
Without the value of b - Insufficient
A
_________________
KUDOS will increase your score
Director  G
Joined: 09 Mar 2018
Posts: 996
Location: India
Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

1
Does (a – 2)(b + 4) = 8?

(1) ab = 2b – 4a
(2) a = 6

Source- Kaplan Mock Test

Does (a – 2)(b + 4) = 8 -------(a)

Statement 1 ab = 2b - 4a

(a) becomes ab + 4a - 2b - 8 = 8
2b - 4a + 4a -2b = 16
0 != 16
Sufficient

Statement 2, a = 6

Though if i substitute this in the question, I can calculate the value of b as - 2,

But question has asked us does (a – 2)(b + 4) = 8, is LHS = RHS

4b + 16 = 8, so now b could have been a fraction, integer or a real number.

Without the value of b we cannot tell that, Hence insufficient

_________________
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.

Originally posted by KanishkM on 20 Jan 2019, 23:16.
Last edited by KanishkM on 21 Jan 2019, 03:40, edited 1 time in total.
Intern  B
Joined: 16 Nov 2018
Posts: 13
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

KanishkM wrote:
Does (a – 2)(b + 4) = 8?

(1) ab = 2b – 4a
(2) a = 6

Source- Kaplan Mock Test

Does (a – 2)(b + 4) = 8 -------(a)

Statement 1 ab = 2b - 4a

(a) becomes ab + 4a - 2b - 8 = 8
2b - 4a + 4a -2b = 16
0 != 16
Sufficient

Statement 2, a = 6

Though if i substitute this in the question, I can calculate the value of b as - 2, But b can be an integer, a number or a real number
Not sufficient

Hi dude,
Can you explain to me your reasoning? If b equals -2; why am I suppose to say that the solution is not correct?

Thank you very much!!!!
Director  G
Joined: 09 Mar 2018
Posts: 996
Location: India
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

oblivion441 wrote:
KanishkM wrote:
Does (a – 2)(b + 4) = 8?

(1) ab = 2b – 4a
(2) a = 6

Source- Kaplan Mock Test

Does (a – 2)(b + 4) = 8 -------(a)

Statement 1 ab = 2b - 4a

(a) becomes ab + 4a - 2b - 8 = 8
2b - 4a + 4a -2b = 16
0 != 16
Sufficient

Statement 2, a = 6

Though if i substitute this in the question, I can calculate the value of b as - 2, But b can be an integer, a number or a real number
Not sufficient

Hi dude,
Can you explain to me your reasoning? If b equals -2; why am I suppose to say that the solution is not correct?

Thank you very much!!!!

I had the same question when i solved this question, but later i realized that the question
was never
1) to find the value of b,
2) then prove that the question stem is true or not.

IMO it was like is LHS = RHS, i should like edit my explanation a bit _________________
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.
Intern  B
Joined: 16 Nov 2018
Posts: 13
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

KanishkM wrote:

I had the same question when i solved this question, but later i realized that the question
was never
1) to find the value of b,
2) then prove that the question stem is true or not.

IMO it was like is LHS = RHS, i should like edit my explanation a bit I understand your point. But if I know that a= 6 and so b=-2 I can answer the question (a – 2)(b + 4) = 8
The only thing that comes in my mind is that we are getting to different results, and this is usually impossible in DS questions.
But I still don't get why b=-2 is not correct. Director  G
Joined: 09 Mar 2018
Posts: 996
Location: India
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

oblivion441 wrote:
KanishkM wrote:

I had the same question when i solved this question, but later i realized that the question
was never
1) to find the value of b,
2) then prove that the question stem is true or not.

IMO it was like is LHS = RHS, i should like edit my explanation a bit I understand your point. But if I know that a= 6 and so b=-2 I can answer the question (a – 2)(b + 4) = 8
The only thing that comes in my mind is that we are getting to different results, and this is usually impossible in DS questions.
But I still don't get why b=-2 is not correct. No worries, I am glad that b = -2, stirred some questions for someone, Nevertheless lets wait for the gc community to reply.

4d, What is your take at this ?

Can you also share your insight on this ??
_________________
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.
Math Expert V
Joined: 02 Sep 2009
Posts: 58381
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

1
1
oblivion441 wrote:
KanishkM wrote:

I had the same question when i solved this question, but later i realized that the question
was never
1) to find the value of b,
2) then prove that the question stem is true or not.

IMO it was like is LHS = RHS, i should like edit my explanation a bit I understand your point. But if I know that a= 6 and so b=-2 I can answer the question (a – 2)(b + 4) = 8
The only thing that comes in my mind is that we are getting to different results, and this is usually impossible in DS questions.
But I still don't get why b=-2 is not correct. b = -2 is not correct because from (2) we don't get that b = -2. THE QUESTION BECOMES: does b = -2? Notice that we are NOT given that (a – 2)(b + 4) = 8. We are asked to answer this.

Does (a – 2)(b + 4) = 8?

Does ab + 4a - 2b = 16?

(1) ab = 2b – 4a --> ab + 4a - 2b = 0. So, the answer to the question is NO: ab + 4a - 2b equals to 0 not 16. Sufficient.

(2) a = 6. The question becomes: does b = -2? We don't know that. Not sufficient.

_________________
Manager  G
Joined: 11 Dec 2013
Posts: 121
Location: India
GMAT Date: 03-15-2015
WE: Education (Education)
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

1
KanishkM oblivion441

The question is Does (a – 2)(b + 4) = 8?
Now when a = 6
Is 4(b+4)=8 ?
If b=-2 , its 8 - YES
If is any other number - NO
In any DS question if you have YES and NO as your answer . Then the data is insufficient .
That means using a=6 , i cannot say whether (a – 2)(b + 4) = 8 or not
Hence insufficient
_________________
KUDOS will increase your score
Intern  B
Joined: 16 Nov 2018
Posts: 13
Re: Does (a – 2)(b + 4) = 8?  [#permalink]

Show Tags

4d wrote:
KanishkM oblivion441

The question is Does (a – 2)(b + 4) = 8?
Now when a = 6
Is 4(b+4)=8 ?
If b=-2 , its 8 - YES
If is any other number - NO
In any DS question if you have YES and NO as your answer . Then the data is insufficient .
That means using a=6 , i cannot say whether (a – 2)(b + 4) = 8 or not
Hence insufficient

Thanks dude,
I got it! Re: Does (a – 2)(b + 4) = 8?   [#permalink] 21 Jan 2019, 07:12
Display posts from previous: Sort by

Does (a – 2)(b + 4) = 8?

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne  