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if x and y are prime, is xy odd ? 1... x - y is even.

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if x and y are prime, is xy odd ? 1... x - y is even. [#permalink] New post 12 Nov 2006, 08:39
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A
B
C
D
E

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if x and y are prime, is xy odd ?

1... x − y is even.
2... x / y is not an integer.

Ο only statement 1 is sufficient to answer the question.
Ο only statement 2 is sufficient to answer the question.
Ο neither statement is sufficient, but together, they are.
Ο statement 1 is very sufficient...and so is statement 2.
Ο no can do.
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 [#permalink] New post 12 Nov 2006, 10:13
C is the answer.

A is not suff. for x=y=2 (st1) holds, and xy is even (for all other options it is indeed odd).

st2 tells us x and y are different.
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 [#permalink] New post 12 Nov 2006, 10:28
if x and y are prime, is xy odd ?

1... x − y is even.
2... x / y is not an integer.

Ο only statement 1 is sufficient to answer the question.
Ο only statement 2 is sufficient to answer the question.
Ο neither statement is sufficient, but together, they are.
Ο statement 1 is very sufficient...and so is statement 2.
Ο no can do.

1) We know that X and Y are prime and there is only 1 even prime. For X-Y to be even both X and Y must be ODD (Cannot have ODD - EVEN to equal EVEN). This means XY will always be ODD. SUFF

2) Only tells us that Y does not go into X or that X < Y but does not tell us anything that will help in answering this questions.

ANSWER = A
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 [#permalink] New post 12 Nov 2006, 10:56
Yes thinking about it x and y can be 2 since it does not say they are different.

If this is the case, then I would go for C, since statement B tells us that the integers are different.
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 [#permalink] New post 12 Nov 2006, 12:12
if x and y are prime, is xy odd ?

1... x − y is even.
2... x / y is not an integer.

for xy to be odd thus all we need to proof is x,y not = 2

x-y is even

thus both are odd OR BOTH ARE TWO ........INSUFF

x/y is not an intiger

either ways any prime is not devisible except by itself and one so deviding any two primes will always yield a non integer ( this includes 2 too)...insuff

BOTH TOGETHER

THEY CANT BE EQUALL THUS MY ANSWER IS C
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Re: DS-Prime [#permalink] New post 13 Nov 2006, 04:47
WinIT wrote:
if x and y are prime, is xy odd ?

1... x − y is even.
2... x / y is not an integer.

Ο only statement 1 is sufficient to answer the question.
Ο only statement 2 is sufficient to answer the question.
Ο neither statement is sufficient, but together, they are.
Ο statement 1 is very sufficient...and so is statement 2.
Ο no can do.


I will take E

1) say x=5 y=3 product is even though their diff is even
say x=7 y=3 product is odd though their diff is even
So A not suff

2) x/y not int.

say x=5 y=3 so 5/3 is not an int

so is 7/3 as above

so E should be it
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 [#permalink] New post 13 Nov 2006, 17:38
C it is..we dont know if X and Y are distinct..
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 [#permalink] New post 13 Nov 2006, 17:41
St1:
We know both x and y must be odd primes. So xy is odd. Sufficient.

St2:
Insufficient. 2/7, 3/5 are all non-integers but the first pair (2 and 7) will yield an even product while the second pair (3 and 5) will yield an odd product.

Ans A
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 [#permalink] New post 13 Nov 2006, 19:50
what if x=2 y=2

x-y=0 which is an even number...

2*2=4 which is even...



ywilfred wrote:
St1:
We know both x and y must be odd primes. So xy is odd. Sufficient.

St2:
Insufficient. 2/7, 3/5 are all non-integers but the first pair (2 and 7) will yield an even product while the second pair (3 and 5) will yield an odd product.

Ans A
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 [#permalink] New post 13 Nov 2006, 19:58
Fell for this! :wall
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 [#permalink] New post 13 Nov 2006, 20:19
Should be A....

0 is not an even number.....
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 [#permalink] New post 14 Nov 2006, 00:59
O is a even number
answer must be C
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 [#permalink] New post 14 Nov 2006, 16:54
OA is C. Thank you all for the explanation.
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 [#permalink] New post 14 Nov 2006, 18:16
Nice explanation Yezz.

I fell for that one...
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  [#permalink] 14 Nov 2006, 18:16
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if x and y are prime, is xy odd ? 1... x - y is even.

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