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confirm pls?

by magical cook » Thu Jan 03, 2008 2:16 pm
If x and y are positive integers and y = √(9 - x) , what is the value of y?
(1) x <8> 1



my answer and OA is different - I want to confirm the answer.
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by camitava » Thu Jan 03, 2008 2:26 pm
Hey Magical cook, if I am not wrong, u have not posted the query correctly. Option - 2 is missing, I think!
Correct me If I am wrong


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Amitava
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by magical cook » Thu Jan 03, 2008 3:14 pm
sorry for some reason form got broken.

Can you take a look?
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by camitava » Thu Jan 03, 2008 3:17 pm
Hey Magical cook, IMO E. By the way, what's the OA?
Correct me If I am wrong


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Amitava
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by StarDust845 » Thu Jan 03, 2008 5:33 pm
Is the answer D?

I am assuming sqrt(4) is +2. We consider only the principal square roots of numbers right?

Calista.
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by magical cook » Thu Jan 03, 2008 7:00 pm
I think E but OA says C....
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by camitava » Thu Jan 03, 2008 7:33 pm
The Qs is saying - X and Y are positive integers and y = sqrt(9 - x). If so and if we go with the OA as C, we can check the values of X and Y.

If X = 1, Y = sqrt(8) ---> Y is not coming as integer
If X = 2, Y = sqrt(7) ---> Y is not coming as integer
If X = 3, Y = sqrt(6) ---> Y is not coming as integer
If X = 4, Y = sqrt(5) ---> Y is not coming as integer
If X = 5, Y = sqrt(4) ---> Y is coming as integer
If X = 6, Y = sqrt(3) ---> Y is not coming as integer
If X = 7, Y = sqrt(2) ---> Y is not coming as integer

So here we go. We can get the unique value of X and Y. So the OA is fine and we took a wrong approach to solve it. So now IMO C. A great miss in our approach - u can say Magical Cook! :cry:
Correct me If I am wrong


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Amitava
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by StarDust845 » Thu Jan 03, 2008 8:17 pm
What are you talking bt?

Given:
a) x and y are positive integers
b) y = sqrt(9-x)

Stmt 1) x < 8
implies x =1,2,...7 now only for x = 5 does y have an integer value. And in GMAT we take sqrt(4) as positive 2. So y = 2. Hence A or D

Note: You can't say "well, we don't know what x is", x MUST have a value so that y is a positive integer. And the only way that can happen is if x = 5 and then y = 2.

Stmt 2) y > 1
implies y = 2,3,4,... but y can't be 3,4,5,6,... because then x must be 0 or negative respectively. But given x is not 0 and not negative. So the only way x can be positive integer is when y = 2.

Hence answer is D. The OA must be wrong.

(I see only one problem.. if the sqrt(4) can be considered +2 or -2 then the answer is C, but sqrt(n) where n is a positive integer is always +ve for GMAT. There is also a thread on that earlier...hmm.. here it is https://www.beatthegmat.com/can-we-consi ... t7618.html).

Calista.
Last edited by StarDust845 on Fri Jan 04, 2008 4:28 pm, edited 3 times in total.
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by camitava » Thu Jan 03, 2008 8:22 pm
StarDust845, sorry sir, my mistake! Ufff, ur first statement - "What r u talking abt" - just put me on the ground otherwise I was flying high!!! :wink: :cry: :lol:
Correct me If I am wrong


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by StarDust845 » Thu Jan 03, 2008 8:27 pm
I apologize. I didn't mean to be disrespectful or anything. I didn't understand what you were saying at all. So I wanted to give a thorough piece by piece approach of how I came to the conclusion (By the way it is maam not sir :) )

Calista.
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by jaiswaln » Fri Jan 04, 2008 7:03 am
Y and X can't be negative hence the possibility of 4^0.5 being -2 is ruled out.

so the answer is D...


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