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NUmber properties [#permalink]

24 Sep 2011, 15:39

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If y not= 3 and 2x/y is a prime integer greater than 2, which of the following must
be true?
I. x = y
II. y = 1
III. x and y are prime integers.
(A) None
(B) I only
(C) II only
(D) III only
(E) I and II
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Re: NUmber properties [#permalink]

24 Sep 2011, 17:44

given 2x/y is prime and greater than 2.

=> 2x/y could be any of the following
3,5,7....
=> 2x/y is odd and prime (as 2 is the only even prime number and its not in this set)

1. x = y , can't be true

if x=y , 2x/y = 2 which is not odd and prime.

2. y=1. can't be true.

if y=1,2x/y = 2x = even which is not odd & prime.

3. x and y are prime integers, need not be true.

lets say 2x/y = 3 and say y=2 prime
=>x = 6/2 = 3 prime
satisfies the given condition here.

but when 2x/y = 3 and y=5 prime

=> x = 15/2 not prime

My Answer is A.

Please post the official answer.

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Re: NUmber properties [#permalink]

24 Sep 2011, 18:09

maheshsrini wrote:

I. x = y. Not true AS 2x/y will become 2

II. y = 1
III. x and y are prime integers.
x=26; y=4; Falsifies both II & III, without violating any of the conditions.

Ans: "A"
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Manager

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Re: NUmber properties [#permalink]

24 Sep 2011, 20:19

I found this problem in the web and did not find the OA. My approach was the same and wanted to confirm the answer.
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Re: NUmber properties [#permalink]

24 Sep 2011, 21:42

"A" from my side as well. No option satisfy the criteria.

Cheers!
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Re: NUmber properties [#permalink] 24 Sep 2011, 21:42

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