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# Is XYZ > 0? 1) XY > 0 2) YZ> 0

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Is XYZ > 0? 1) XY > 0 2) YZ> 0 [#permalink]

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07 Jan 2006, 15:13
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Is XYZ > 0?

1) XY > 0

2) YZ> 0
Intern
Joined: 13 Nov 2005
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07 Jan 2006, 16:14
I'd say E - both (1) and (2) are not sufficient to conclude that xyz > 0 because:

For xyz > 0, either x,y,z > 0 or any two are < 0 and the third > 0

(1) says xy > 0 but says nothing about z - so its not sufficient by itself
(2) says yz > 0 but again says nothing about x - so its not sufficient by itself

Therefore, answer is either C or E.

If xy > 0 either x and y are both > 0 or x and y are both < 0.

Case 1:
x and y are both > 0
Then z is also > 0 (since yz > 0 from (2))
And xyz will be > 0

Case 2:
x and y are both < 0
Then z must be < 0 (since yz > 0 from (2)
And xyz will be < 0

Hence (1) and (2) together are not sufficient.

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08 Jan 2006, 22:37
(1) Insufficient. Z could be negative.
(2) Insufficient. X could be negative.

Using (1) and (2), insufficient, X,Y and Z could all be negative or positive.

Ans E
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08 Jan 2006, 23:01
E for me too

A) Insifficeint
B)Insufficient

Both : becomes negative if all 3 are negative and positive if all 3 postive..so Insifficient
08 Jan 2006, 23:01
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