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Is the product abcd negative?

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Is the product abcd negative?  [#permalink]

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New post 23 Nov 2016, 02:15
1
1
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

57% (01:07) correct 43% (01:01) wrong based on 123 sessions

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Senior Manager
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Joined: 06 Jun 2016
Posts: 258
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]

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New post 23 Nov 2016, 02:41
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
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Re: Is the product abcd negative?  [#permalink]

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New post 23 Nov 2016, 18:17
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
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Re: Is the product abcd negative?  [#permalink]

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New post 31 Mar 2018, 13:58
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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

Answer: C

Cheers,
Brent
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Re: Is the product abcd negative?  [#permalink]

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New post 01 Apr 2018, 05:31
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

Answer: C
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Re: Is the product abcd negative? &nbs [#permalink] 01 Apr 2018, 05:31
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