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For any numbers x#y = xy - x - y . If x#y = 1 , which of the

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Joined: 11 May 2008
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For any numbers x#y = xy - x - y . If x#y = 1 , which of the [#permalink]

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New post 25 Aug 2008, 03:38
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For any numbers x#y = xy - x - y . If x#y = 1 , which of the following cannot be the value of y ?


* -2
* -1
* 0
* 1
* 2

why is A not the soln??

Kudos [?]: 216 [0], given: 0

Manager
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Joined: 15 Jul 2008
Posts: 206

Kudos [?]: 66 [0], given: 0

Re: variable... [#permalink]

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New post 25 Aug 2008, 04:16
arjtryarjtry wrote:
For any numbers x#y = xy - x - y . If x#y = 1 , which of the following cannot be the value of y ?


* -2
* -1
* 0
* 1
* 2

why is A not the soln??


the question does not say that x, and y are integers. So y=-2 is possible. Here what you need to do is put xy-x-y=1 and try out different values of y.
with y=-2, u get x=1/3. So y can be -2.

Answer is 1. if y=1, then you get -1=1 which is not possible.

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Director
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Schools: Wharton
Re: variable... [#permalink]

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New post 25 Aug 2008, 04:23
arjtryarjtry wrote:
For any numbers x#y = xy - x - y . If x#y = 1 , which of the following cannot be the value of y ?


* -2
* -1
* 0
* 1
* 2

why is A not the soln??


1 = xy - x - y
1 = x(y-1) - y
y + 1 = x(y-1)

Thus, y cannot be 1.
If y = 1, y+1 = 2 and x(y-1) = 0

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Re: variable... [#permalink]

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New post 25 Aug 2008, 06:32
For any numbers x#y = xy - x - y . If x#y = 1 , which of the following cannot be the value of y ?


* -2
* -1
* 0
* 1
* 2

Here we have x#y = 1
which means
xy - x - y = 1
or, xy - x = 1 + y
or, x(y-1) = 1 + y
or, x = (1 + y)/(y - 1)

x will be undefined if y - 1 = 0
or y = 1

and if we substitute y = -2
we get x = 1/3

and x#y = 1
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Re: variable...   [#permalink] 25 Aug 2008, 06:32
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For any numbers x#y = xy - x - y . If x#y = 1 , which of the

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