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If y ≠ 3 and 3x/y is a prime integer greater than 2,

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Manager
Joined: 29 Jul 2007
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If y ≠ 3 and 3x/y is a prime integer greater than 2, [#permalink]

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26 Nov 2007, 15:57
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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) Ⅱ only
D) Ⅲ only
E) Ⅰ and Ⅲ

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CEO
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26 Nov 2007, 16:05
B.

1. if x<y> 3*n - is not a prime. so x=y. suff.
2. for (1,1) y=1 but for (2,2) y=2 insuff.
3. for (2,2) x,y - prime but for (4,4) x,y - not prime. insuff.

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26 Nov 2007, 16:07
Skewed wrote:
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) Ⅱ only
D) Ⅲ only
E) Ⅰ and Ⅲ

must be!!! hmmm.................

ok, then it is B. I only because if x and y are cancelled out then only 3x/y remains a prime.

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Manager
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26 Nov 2007, 16:24
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

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26 Nov 2007, 17:25
Skewed wrote:
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

thats why the question says that y is not equal to 3.

though thats a good point.

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CEO
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26 Nov 2007, 17:28
hm... A is reasonably.

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Intern
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26 Nov 2007, 17:31
Skewed wrote:
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

In case I, Y has to be equal to X.

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26 Nov 2007, 17:32
Skewed wrote:
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

Thats pretty good.

Tiger he says that (3*5/3)/1 X=5/3. So A looks good.

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Director
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26 Nov 2007, 17:33
B it is,

was going to say E..

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Director
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26 Nov 2007, 17:37
GMATBLACKBELT wrote:
Skewed wrote:
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

Thats pretty good.

Tiger he says that (3*5/3)/1 X=5/3. So A looks good.

from the question:

3x=y*prime number-----> either y=3 or prime number=3

y is not 3, thus Prime number= 3----> 3x=y3---->x=y, where x and y are not necessarily prime numbers.

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Manager
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26 Nov 2007, 18:59

Ⅱ only!

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Senior Manager
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26 Nov 2007, 19:05
Skewed wrote:
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

Good point was going for B..

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Director
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26 Nov 2007, 19:22
Skewed wrote:
What about [(5/3),1] for x,y in case I?

[3*(5/3)]/1= 5

A.

it was not mentioned that x is an intenger...missed this point

vote for A

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Senior Manager
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26 Nov 2007, 20:06
agh! the simple ones...

how do one avoid felling for these tricks?

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Director
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26 Nov 2007, 20:17
asdert wrote:
agh! the simple ones...

how do one avoid felling for these tricks?

"assumed to be possible unless stated or proved otherwise"

unless it says that a number is not a ratio, same as to say that a number is an intenger (as in the example above), we can correctly assume that the number is a ratio ..

simple indeed,

i fell for too

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Intern
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27 Nov 2007, 07:17
It is A.

x=1/3
Y=1/5

3x/y = 5 which is prime

so x != y

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27 Nov 2007, 12:49
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

for 3x/y to be prime , x/y must = 1

i believe it is A

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SVP
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16 Dec 2007, 09:38
did we get a final consensus on this one ?

I am getting A. Here is why.

Q basically tells us that 3x/y =3,5,7,9, ...

1 says x must equal y. not true, because if 3x/y=5, we just get 3x=5y. not always true

2 says y must be 1. again, from above, we can see it doesnt have to be the case.

3. x and y must be prime. i dont think they do, just by looking at the above.

so since none fit the bill, i went with A

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Manager
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16 Dec 2007, 09:56
it is obviously A:

Pick numbers: x=14, y=6
3*14/6=7. None of the choices works. And no restrictions on x=14 and y=6

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Re: prime integer   [#permalink] 16 Dec 2007, 09:56
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If y ≠ 3 and 3x/y is a prime integer greater than 2,

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