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I do not understand this question

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Senior | Next Rank: 100 Posts
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by jfranco23 » Mon Jan 19, 2009 1:12 pm
Hi All,

I want to know if someone can give the explanation of this question:

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

Thanks
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by Hovey25 » Mon Jan 19, 2009 1:35 pm
D...

I plugged in starting w/ the middle answer...product must total 6 (factors of 1,6 and 3,2)

1 + 3 + 2 +(3*2)=12
1 + 1 +6 + (6*1)=14...NO

Go to the next biggest since the answer was not quite large enough...

8 (factors of 1,8 and 2,4)

1 + 4 + 2 + (4*2)=15 DING!
to follow through 1 + 1 + 8 + (8*1)=18 No.

Maybe not the best way, sorry if it isn't descriptive enough, that was the easiest way I saw.
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by hypik21 » Mon Jan 19, 2009 2:33 pm
wouldnt it be C then...2+4=6
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by jfranco23 » Mon Jan 19, 2009 2:57 pm
I think the right way is as Hovey25 describe it, but we are not looking for the prOduct, we are looking for the sum so to get a 6 you can use 4 and 2, the right answer is C.
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by Hovey25 » Tue Jan 20, 2009 7:08 am
You are right, careless error... :oops:

Sorry
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by aroon7 » Thu Jan 22, 2009 9:36 pm
1+x+y+xy = 15
(1+x) + y(1+x) = 15
(1+x)(1+y)=15

we have 2 options
5*3 or 15*1
15*1 wont work, since y will be zero (but x & y are +ve integers)

1+x = 5
1+y = 3

so X+Y =6

HTH
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i am back!
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