If xy > 0, does (x 1)(y 1) = 1? (1) x + y = xy (2) x = y : DS Archive
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# If xy > 0, does (x 1)(y 1) = 1? (1) x + y = xy (2) x = y

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If xy > 0, does (x 1)(y 1) = 1? (1) x + y = xy (2) x = y [#permalink]

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05 Nov 2004, 15:15
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If xy > 0, does (x â€“ 1)(y â€“ 1) = 1?

(1) x + y = xy
(2) x = y
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05 Nov 2004, 15:37
Maybe is it too obvious but I choose A
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05 Nov 2004, 15:57
A

(x â€“ 1)(y â€“ 1) = xy - x - y + 1

1) xy = x + y
substitute in
x + y - x - y + 1
expression you are left out with is 1
sufficient

2) x^2 - x - x + 1
The x's don't cancel out to leave 1 as answer because what you want is when you cancel out everything, you are left with only 1. Only 1) gives you that.
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Best Regards,

Paul

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05 Nov 2004, 16:21
Great job, A is OA.

I know this is an easy one but thought there was trick in there,.. with Paul's explanation, there shouldn't be any doubt that A is sufficient.
05 Nov 2004, 16:21
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