is x>0?

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by Anju@Gurome » Wed Mar 13, 2013 9:04 pm
paresh_patil wrote:xyz>0, is x>0?
1) xy>0
2) xz>0
Statement 1: x and y are of same sign.
Also xy and xyz are of same sign.
Hence, z > 0
But we cannot conclude anything about x.

Not sufficient

Statement 2: x and z are of same sign.
Also xz and xyz are of same sign.
Hence, y > 0
But we cannot conclude anything about x.

Not sufficient

1 & 2 Together: Now we know, both y and z are positive and x is of same sign as of y and z.
Hence, x > 0

Sufficient

The correct answer is C.
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by srcc25anu » Thu Mar 14, 2013 4:10 am
Given XYZ = +ve

Stat 1: xy>0 X .... Y .... Z .... XYZ ... Is X positive?
_______ +ve .... +ve ... +ve ... +ve ....... Yes
_______ -ve .... -ve ... +ve ... +ve ....... No
hence Insufficient

Stat 2: xz>0 X .... Y .... Z .... XYZ .... Is X positive?
________ +ve ... +ve ... +ve ... +ve ....... Yes
_______ -ve ... +ve ... -ve ... +ve ....... No
hence Insufficient

Together: only possible for XYZ >0 when all three are positive.

Hence X is positive.
Answer C