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Prime numbers

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by oks » Sun May 17, 2009 2:02 pm
If y ≠ 3 and 3x/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) Ⅱonly
(D) Ⅲonly
(E) Ⅰand Ⅲ

OA is A, but why not B? If x = y, then 3x/y will be always 3, which is a prime and greater than 2. Could someone explain what I am missing?

Thanks!
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by ssmiles08 » Sun May 17, 2009 8:36 pm
Let's say x = 22 and y = 6

3*(22/6) = 11 ---> which is a prime integer greater than 2

In this case

x does not have to equal y
y does not have to equal 1
x and y are both non-prime numbers


so all three of them could be true but neither possibility is a must have

I am not sure what your question is asking but I hope this clarifies it
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by sanju09 » Mon May 18, 2009 5:03 am
ssmiles08 wrote:Let's say x = 22 and y = 6

3*(22/6) = 11 ---> which is a prime integer greater than 2

In this case

x does not have to equal y
y does not have to equal 1
x and y are both non-prime numbers


so all three of them could be true but neither possibility is a must have

I am not sure what your question is asking but I hope this clarifies it
Great deal ssmiles08, you got the best way to crack a "must be true" problem on GMAT, just one possibility that denies all. Fantastic! But what prevents you answer "None" now?
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
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