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If xy > 0, does (x – 1)(y – 1) = 1? (1) x + y = xy (2) x = y

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Joined: 20 Feb 2012
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If xy > 0, does (x – 1)(y – 1) = 1? (1) x + y = xy (2) x = y [#permalink] New post 23 Feb 2012, 23:33
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Difficulty:

  45% (medium)

Question Stats:

63% (01:45) correct 37% (01:04) wrong based on 30 sessions
If xy > 0, does (x – 1)(y – 1) = 1?

(1) x + y = xy

(2) x = y
[Reveal] Spoiler: OA
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Re: does (x – 1)(y – 1) = 1? [#permalink] New post 23 Feb 2012, 23:38
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Expert's post
BANON wrote:
If xy > 0, does (x – 1)(y – 1) = 1?

(1) x + y = xy

(2) x = y


If \(xy>0\) does \((x-1)(y-1)=1\)?

Question: is \((x-1)(y-1)=1\)? --> is \(xy-x-y+1=1\)? is \(x+y=xy\)?

(1) \(x+y=xy\) --> directly gives us the answer YES. Sufficient.

(2) \(x=y\) --> question becomes: is \(x+x=x^2\)? --> is \(x(x-2)=0\)? --> is \(x=0\) or \(x=2\)? --> since given that \(xy>0\), then \(x\neq{0}\), so the question becomes is \(x=2\)? We don't know that, hence this statement is not sufficient.

Answer: A.

Hope it's clear.
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Intern
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Joined: 20 Feb 2012
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Kudos [?]: 160 [0], given: 6

Re: does (x – 1)(y – 1) = 1? [#permalink] New post 24 Feb 2012, 00:03
thank u BUNUEL :-D for ur instant reply's

after ur explanation's they all seem like sub par questions.
Re: does (x – 1)(y – 1) = 1?   [#permalink] 24 Feb 2012, 00:03
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