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a ps from gmat club

by diebeatsthegmat » Sat Feb 05, 2011 1:03 am
If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.
(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢

why A? i answered it B . is it not right that 3x/y=3 since x=y? and 3>2 and its fit to the condition!
i dont understand. can you guy please explain?
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by Night reader » Sat Feb 05, 2011 1:37 am
It's theoretically A - none; two ways I used to solve and subsequently to check --> algebraic and plug-in

algebraic, follow the conditions given 3x/y is a MUST prime >2, so we consider this as a whole expression
plug-in --> (I) x=5/3, y=1 and 3x/y=3*5/3 : 1=3
(II) y=1, 3x/y is not always prime then
(III) x,y prime integers --> x=4,y=4, 3x/y=3*4/4=3

All three choices are voided.
diebeatsthegmat wrote:If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.
(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢

why A? i answered it B . is it not right that 3x/y=3 since x=y? and 3>2 and its fit to the condition!
i dont understand. can you guy please explain?
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by sanju09 » Sat Feb 05, 2011 1:55 am
diebeatsthegmat wrote:If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.
(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢

why A? i answered it B . is it not right that 3x/y=3 since x=y? and 3>2 and its fit to the condition!
i dont understand. can you guy please explain?

If y ≠ 3 and 3 x/y is still a prime integer greater than 2, then the general perception is that x is got to be a multiple of y, and the quotient x/y cannot be anything other than 1 in order to keep 3 x/y a prime greater than 2. This is where anybody could fall in the trap that x = y, what if x = 1/3 and y = 1/5, nowhere in the question is said that x and y are integers. Hence

[spoiler](A) None[/spoiler]
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by winnerhere » Sat Feb 05, 2011 4:24 am
None

y = 6 ; x = 2...which cancels all other options and leaves with none
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by sanju09 » Sat Feb 05, 2011 4:34 am
winnerhere wrote:None

y = 6 ; x = 2...which cancels all other options and leaves with none
But this won't make 3 x/y a prime integer greater than 2.
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by GMATGuruNY » Sat Feb 05, 2011 4:42 am
diebeatsthegmat wrote:If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.
(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢

why A? i answered it B . is it not right that 3x/y=3 since x=y? and 3>2 and its fit to the condition!
i dont understand. can you guy please explain?
Plug in x = 10, y = 6.
This combination works: 3x/y = (3*10)/6 = 5.
Eliminate I, II, III.

The correct answer is A.
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by diebeatsthegmat » Sun Feb 06, 2011 12:18 pm
GMATGuruNY wrote:
diebeatsthegmat wrote:If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.
(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢

why A? i answered it B . is it not right that 3x/y=3 since x=y? and 3>2 and its fit to the condition!
i dont understand. can you guy please explain?
Plug in x = 10, y = 6.
This combination works: 3x/y = (3*10)/6 = 5.
Eliminate I, II, III.

The correct answer is A.
if x= 10 and y =6 , x >y, x is not equal y anymore.
i dont understand...
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