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Re: If XYZ>0 is X>0 [#permalink]
11 Apr 2011, 08:51
1) x and y both are positive or negative, so x could be -ve, or +ve insuff. 2) x and z both are positive or negative, so x could be -ve, or +ve insuff.
For C as xyz > 0, so if y and z both -ve, then x has to be +ve, and if y and z become +ve then x has to be +ve to become xyz > 0. _________________
Re: If XYZ>0 is X>0 [#permalink]
11 Apr 2011, 10:54
2
This post received KUDOS
1
This post was BOOKMARKED
Following chart lists down the possible scenarios in which XYZ > 0
X Y Z 1) - - + 2) - + - 3) + - - 4) + + +
As per statement I --> 1 & 4 have to be true for XY > 0. So I alone is insufficient as X can be +ve or -ve As per statement II --> 2& 4 have to be true for XZ > 0 So II alone is insufficient as X can be +ve or -ve If we combine both statements then only 4 is true and X has to be +ve
Re: If XYZ>0 is X>0 [#permalink]
11 Apr 2011, 12:43
2
This post received KUDOS
Expert's post
1
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DestinyChild wrote:
If XYZ>0 is X>0
XY > 0 XZ > 0
Obviously the answer is Yes or No; Get your kudos for reasoning out why the answer is C and keep an eye on time too
Triple kudos for someone suggesting quicker technique for DS stems with triple variables...!
Certainly each statement is not sufficient alone (the logic is identical for each: for S1, x and y can both be negative or both positive, and for S2, x and z can both be negative or both positive). You might notice that S1 tells us z is positive, and S2 tells us y is positive, but that's not what we're looking for.
Now, together, the inequality xy > 0 means 'x and y have the same sign'. So from the two statements we know x and y have the same sign, and x and z have the same sign, so x, y and z all have the same sign. If xyz > 0, they must all be positive, and the answer is C. _________________
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Re: If XYZ>0 is X>0 [#permalink]
11 Apr 2011, 17:41
C. For XYZ > 0 either all are positive or two of them negative. From St1 and St2 it is clear that both xy and xz has to be positive or both xz and xy has to be negative. in the latter case XYZ > 0 will be false.
Re: If xyz > 0, is x > 0? (1) xy > 0 (2) xz > 0 [#permalink]
18 Nov 2013, 07:29
Hello from the GMAT Club BumpBot!
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Re: If xyz > 0, is x > 0? (1) xy > 0 (2) xz > 0 [#permalink]
26 Dec 2014, 09:21
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).
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Re: If xyz > 0, is x > 0? (1) xy > 0 (2) xz > 0 [#permalink]
09 Jan 2016, 20:53
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).
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