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    Strategies and techniques for approaching featured GMAT topics

If xy > 0, is xyz < 0?

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If xy > 0, is xyz < 0?  [#permalink]

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New post 22 Apr 2016, 03:32
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

70% (01:35) correct 30% (01:15) wrong based on 124 sessions

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Re: If xy > 0, is xyz < 0?  [#permalink]

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New post 22 Apr 2016, 11:02
1
xy > 0 --> x and y have the same signs
Is xyz < 0?

St1: xz > 0 --> x and z have the same signs
Suppose x = +ve --> y = +ve and z = +ve --> Is xyz < 0? No
Suppose x = -ve --> y = -ve and z = -ve --> Is xyz < 0? Yes
Not Sufficient

St2: yz > 0 --> y and z have the same signs
Suppose y = +ve --> x = +ve and z = +ve --> Is xyz < 0? No
Suppose y = -ve --> x = -ve and z = -ve --> Is xyz < 0? Yes
Not Sufficient

Combining St1 and St2: xy > 0; xz > 0; yz > 0
x = +ve --> y = +ve and z = +ve
x = -ve --> y = -ve and z = -ve
Still not sufficient

Answer: E
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If xy > 0, is xyz < 0?  [#permalink]

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New post 30 Aug 2018, 05:24
niks18 VeritasKarishma chetan2u pushpitkc


Quote:
If xy > 0, is xyz < 0?

(1) xz > 0
(2) yz > 0


Is it appropriate to combine two statements
as:
xy \(z^2\) > 0

I incorrectly chose (C) here
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Re: If xy > 0, is xyz < 0?  [#permalink]

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New post 30 Aug 2018, 05:31
1
adkikani wrote:
niks18 VeritasKarishma chetan2u pushpitkc


Quote:
If xy > 0, is xyz < 0?

(1) xz > 0
(2) yz > 0


Is it appropriate to combine two statements
as:
xy \(z^2\) > 0

I incorrectly chose (C) here


Hi adkikani

Even if you combine the two statements you cannot arrive at xyz<0.

It is given that xy>0, so you simply need to know whether z<0 and on combining you will not get this information

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Re: If xy > 0, is xyz < 0?  [#permalink]

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New post 30 Aug 2018, 05:49
1
adkikani wrote:
niks18 VeritasKarishma chetan2u pushpitkc


Quote:
If xy > 0, is xyz < 0?

(1) xz > 0
(2) yz > 0


Is it appropriate to combine two statements
as:
xy \(z^2\) > 0

I incorrectly chose (C) here


So when you get xyz^2>0, it just tells you xy>0..
But if all three are negative..xyz^2 will be >0 but xyz<0..
However if all three are positive..xyz^2 will be >0 and xyz>0
So different answers
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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Re: If xy > 0, is xyz < 0?  [#permalink]

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New post 30 Aug 2018, 06:05
Bunuel wrote:
If xy > 0, is xyz < 0?

(1) xz > 0
(2) yz > 0


xy > 0 -> x and y have same signs

(1) xz > 0 -> x and z have same signs -> x, y, z have same signs. If all 3 variables are negative -> Yes. If all 3 variables are positive -> No. --> Not sufficient.
(2) yz > 0 -> y and z have same signs -> x, y, z have same signs. If all 3 variables are negative -> Yes. If all 3 variables are positive -> No. --> Not sufficient.
(1)+(2) x, y, z have same signs -> Not sufficient.

Answer E.
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Re: If xy > 0, is xyz < 0? &nbs [#permalink] 30 Aug 2018, 06:05
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