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If x and y are positive integers and 1 + x + y + xy = 15,

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If x and y are positive integers and 1 + x + y + xy = 15, [#permalink]

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New post 08 Oct 2008, 11:06
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If x and y are positive integers and 1 + x + y + xy = 15, what is the value of x + y?
A. 3
B. 5
C. 6
D. 8
E. 9

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Re: PS question [#permalink]

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New post 08 Oct 2008, 12:43
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rnemani wrote:
If x and y are positive integers and 1 + x + y + xy = 15, what is the value of x + y?
A. 3
B. 5
C. 6
D. 8
E. 9


x + y = 15 - 1
x + y + xy = 14

- x or y cannot be an odd number because it will make the equation false.
- The, test the equation with even numbers
x = 2 , y = 4
2 + 4 - 2*4 = 14
True

x + y = 6

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Re: PS question [#permalink]

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New post 09 Oct 2008, 05:35
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Its (C) for sure

take x+y = 6 (x=4 and y=2 or vice versa)

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Re: PS question [#permalink]

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New post 10 Oct 2008, 01:52
Yes, C.

1+x +y + xy = 15
or (1+x)(1+y) = 3*5 and hence, either x = 2, y = 4 or x = 4, y =2...and x + y = 6.

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Re: PS question [#permalink]

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New post 10 Oct 2008, 01:57
1+x+Y+xy = 15
=> (1+x)(1+y) = 15
=> x=2 & y = 4 OR vice-versa

so X+Y = 6

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Re: PS question   [#permalink] 10 Oct 2008, 01:57
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If x and y are positive integers and 1 + x + y + xy = 15,

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