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If zy < xy < 0, is xz + x = z? (1) z<x>0 [#permalink]
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13 May 2007, 12:40
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If zy < xy < 0, is xz + x = z?
(1) z<x>0
OA is D



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Joined: 17 Apr 2007
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oops...should be
(1) z is less than x
(2) y is greater than 0
Last edited by kookoo4tofu on 13 May 2007, 12:42, edited 1 time in total.



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can you post the rest of the question?



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xz + x = z
can be rewritten as
xz = zx
Statement 1
whenever statement 1 is true zx is negative.
xz can never be negative
so we can say for sure that when z is less then x , the inequality is false.
sufficient
Statement 2
when y is grater then 0 then x,z have to be negative.
if x,z are negative and y is positive
when zy < xy < 0
then z<x
same info & logic as statement 1
sufficient
so the answer is (D).
Last edited by KillerSquirrel on 13 May 2007, 13:39, edited 1 time in total.



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i. is not sufficient. you above KillerSquirrel have illustrated a case in which the questioned equation results in false. I'll illustrate one in which the questioned equation results in true: z = 3, x = 2, y = 1.  x  z  =
 z    x .......So in this case,  2  ( 3)  =  3     2, 1=1. So, of course, if we have one answer in which we get true and one in which we get false, statement i is insufficient. I get E as the answer then. Because you spotted that statement ii is equivalent to i. I didn't catch that part. I thought at first B was the answer.



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ethan_casta wrote: i. is not sufficient. you above KillerSquirrel have illustrated a case in which the questioned equation results in false. I'll illustrate one in which the questioned equation results in true: z = 3, x = 2, y = 1.  x  z  =  z    x .......So in this case,  2  ( 3)  =  3     2, 1=1. So, of course, if we have one answer in which we get true and one in which we get false, statement i is insufficient. I get E as the answer then. Because you spotted that statement ii is equivalent to i. I didn't catch that part. I thought at first B was the answer.
Actually, it's always true ... For statment (1) & (2)... Have a look at my link



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ethan_casta wrote: i. is not sufficient. you above KillerSquirrel have illustrated a case in which the questioned equation results in false. I'll illustrate one in which the questioned equation results in true: z = 3, x = 2, y = 1.  x  z  =  z    x .......So in this case,  2  ( 3)  =  3     2, 1=1. So, of course, if we have one answer in which we get true and one in which we get false, statement i is insufficient. I get E as the answer then. Because you spotted that statement ii is equivalent to i. I didn't catch that part. I thought at first B was the answer.
yes ! you are right my logic is "non sequitur"



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Re: GMATPrep: abs [#permalink]
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13 May 2007, 14:51
kookoo4tofu wrote: If zy < xy < 0, is xz + x = z?
(1) z is less than x (2) y is greater than 0 OA is D
from i, if z is less than x, then x and z are ve and y is +ve.. suff
from ii, if y is +ve, then again x and z are ve and it is also sufficient.
So D.



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Abs value [#permalink]
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13 May 2007, 15:07
Himalayan, the question is not that simple unfortunately.



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zy<xy<0...This means that z<x<0>0 and z>x>0 if y<0. In other words, both z and x have to be the same sign.
[1] z<x>0 Both z and x are negative  sufficient.
[2] kookoo4tofu wrote "y is greater than 0", but I believe the correct stmt is y<0. Using this stmt, both z and x are positive and therefore sufficient.
Answer: D



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Abs value [#permalink]
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13 May 2007, 15:24
didn't you guys see that two cases have been advanced in which statement i produces a result of true and also a result of false? that disproves your claim.



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i checked the question again and statement 2 does say "y greater than zero"



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Re: Abs value [#permalink]
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14 May 2007, 18:48
ethan_casta wrote: Himalayan, the question is not that simple unfortunately.
you are right. i just laid down what i had in a quick calculation in my mind.










