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# The operation is defined by x y = 1/x + 1/y for all nonzero

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Director
Joined: 29 Aug 2005
Posts: 832
The operation is defined by x y = 1/x + 1/y for all nonzero [#permalink]

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15 Nov 2008, 15:08
The operation Θ is defined by x Θ y = 1/x + 1/y for all nonzero numbers x and y. If z is a
number greater than 1, which of the following must be true?
I. x Θ (-z) = 0
II. z Θ z/(z-1)= 1
III.2/z Θ 2/z= z
A. I only
B. I and II only
C. I and III only
D. II and III only
E. I, II, and III

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VP
Joined: 05 Jul 2008
Posts: 1367
Re: GMAT Set: 28 -34 [#permalink]

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15 Nov 2008, 16:20
Got D II and III

I says (1/x) - (1/z) = 0 means z-x=0 and z=x. not necessary

II. z Θ z/(z-1)= 1

1/z + (z-1)/z = 1/z (z-1+1) = 1 Yes

III.2/z Θ 2/z= z

z/2 + z/2 = z
Intern
Joined: 28 Jul 2008
Posts: 30
Re: GMAT Set: 28 -34 [#permalink]

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16 Nov 2008, 00:36
1) is still wrong. The difference is not necessarily equal to zero. So, IMO = D

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Re: GMAT Set: 28 -34   [#permalink] 16 Nov 2008, 00:36
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# The operation is defined by x y = 1/x + 1/y for all nonzero

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