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

 It is currently 15 Oct 2019, 05:17 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.  Is the product abcd negative?

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

Hide Tags

Math Expert V
Joined: 02 Sep 2009
Posts: 58333
Is the product abcd negative?  [#permalink]

Show Tags

1
4 00:00

Difficulty:   45% (medium)

Question Stats: 56% (01:08) correct 44% (01:12) wrong based on 160 sessions

HideShow timer Statistics

Is the product abcd negative?

(1) a < b < c < d
(2) ad > 0

_________________
Senior Manager  Joined: 06 Jun 2016
Posts: 256
Location: India
Concentration: Operations, Strategy
Schools: ISB '18 (D)
GMAT 1: 600 Q49 V23 GMAT 2: 680 Q49 V34 GPA: 3.9
Re: Is the product abcd negative?  [#permalink]

Show Tags

Bunuel wrote:
Is the product abcd negative?

(1) a < b < c < d
(2) ad > 0

IMO C

Clearly statement 1 is insufficient.

From statement 2
we know a and d have same signs
but we don't know anything about b and c
Hence insufficient

Combining
a < b < c < d and ad > 0
we can say that abcd= positive
VP  D
Joined: 05 Mar 2015
Posts: 1013
Re: Is the product abcd negative?  [#permalink]

Show Tags

1
Bunuel wrote:
Is the product abcd negative?

(1) a < b < c < d
(2) ad > 0

(1) a could be negative and b,c,d be +ve ------Yes
all a,b,c,d could be +ve-----------------------No
insuff..

(2) a and D are of same sign
no info on b,c--------Not suff

Combining we know all a,b,c,d are on either right side or left side of 0
any case product is +ve
suff

Ans C
GMAT Club Legend  V
Joined: 12 Sep 2015
Posts: 4000
Re: Is the product abcd negative?  [#permalink]

Show Tags

1
Top Contributor
Bunuel wrote:
Is the product abcd negative?

(1) a < b < c < d
(2) ad > 0

Target question: Is the product abcd negative?

Statement 1: a < b < c < d
This statement doesn't FEEL sufficient, so I'll TEST some values.
There are several values of a, b, c, and d that satisfy statement 1. Here are two:
Case a: a = -1, b = 1, c = 2 and d = 3. In this case, abcd = (-1)(1)(2)(3) = -6. So, the answer to the target question is YES, the product abcd is negative
Case b: a = -2, b = -1, c = 2 and d = 3. In this case, abcd = (-2)(-1)(2)(3) = 12. So, the answer to the target question is NO, the product abcd is not negative
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Aside: For more on this idea of testing values when a statement doesn't feel sufficient, read my article: http://www.gmatprepnow.com/articles/dat ... lug-values

Statement 2: ad > 0
Since there's no information about b and c, there's no way to determine whether the product abcd is negative
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 2 tells us that ad > 0
This means that EITHER a and d are both negative OR a and d are both positive.
Let's examine each case separately...

Case a: a and d are both negative. We also know that a < b < c < d. We can see that d is the greatest value. So, if d is negative, then a, b and c are also negative.
So, the product abcd = (NEGATIVE)(NEGATIVE)(NEGATIVE)(NEGATIVE) = POSITIVE. So, in this case, the answer to the target question is YES, the product abcd is negative

Case b: a and d are both positive. We also know that a < b < c < d. We can see that a is the least value. So, if a is positive, then b, c and d are also positive.
So, the product abcd = (POSITIVE)(POSITIVE)(POSITIVE)(POSITIVE) = POSITIVE. So, in this case, the answer to the target question is YES, the product abcd is negative

There are only two possible cases (above), and in each case the answer to the target question is the same: YES, the product abcd is negative
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Cheers,
Brent
_________________
SVP  V
Joined: 26 Mar 2013
Posts: 2345
Re: Is the product abcd negative?  [#permalink]

Show Tags

Bunuel wrote:
Is the product abcd negative?

(1) a < b < c < d
(2) ad > 0

(1) a < b < c < d

Let a = 1 & b = 2 & c =3 & d=4...........Answer is No

Let a =-1 & b = 2 & c =3 & d=4...........Answer is Yes

Insufficient

(2) ad > 0

It tells us the both a & d have the same sign.
No info about b & c

Insufficient

Combine 1 & 2

If a & d are positive......... b & d are positive as well...............Answer is No

If a & d are negative......... b & d are negative as well...............Answer is No

Sufficient

Non-Human User Joined: 09 Sep 2013
Posts: 13160
Re: Is the product abcd negative?  [#permalink]

Show Tags

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________ Re: Is the product abcd negative?   [#permalink] 12 Aug 2019, 18:41
Display posts from previous: Sort by

Is the product abcd negative?

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

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