Is a product of three integers XYZ a prime? (1) X=Y (2) Z=1 : DS Archive
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# Is a product of three integers XYZ a prime? (1) X=Y (2) Z=1

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Is a product of three integers XYZ a prime? (1) X=Y (2) Z=1 [#permalink]

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19 Jun 2003, 07:18
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Is a product of three integers XYZ a prime?

(1) X=–Y
(2) Z=1
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19 Jun 2003, 11:29
C?

From 1, maybe or maybe not
From 2, nothing

Together, you now it is impossible to get a prime
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19 Jun 2003, 14:33
Ans : C

1) Z could be -ve thus => insuff
2) X*Y could be prime => insuff

Combined :

X*Y*Z = -ve number

and since X=-Y, X*X can never be prime

Ans NO => Suff
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19 Jun 2003, 21:37
tzolkin wrote:
Ans : C

1) Z could be -ve thus => insuff
2) X*Y could be prime => insuff

Combined :

X*Y*Z = -ve number

and since X=-Y, X*X can never be prime

Ans NO => Suff

You move in the right direction, either set is not sufficient. Combine -- the product is –X^2, a negative number can NEVER be a prime! If X=0, then tha product is 0, which is not prime either. Thus, C.
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06 Feb 2007, 11:03
I would say this has to be B...

x*y*z=prime?

1) x=-y, lets see if x=2, then y=-2 x*y=-4*if z=-1 then product not a prime..suppose x=-1 y=1 then -1*z if z=-3 then product is 3 (prime) Insuff

2) z=1, taking above example.....

1*-2*2=-4 not a prime..you can try other numbers...it will always never be a prime..B has to be it...

I wish styolar was around..to verify.but i think B is the right
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06 Feb 2007, 11:29
fresinha12 wrote:
I would say this has to be B...

x*y*z=prime?

1) x=-y, lets see if x=2, then y=-2 x*y=-4*if z=-1 then product not a prime..suppose x=-1 y=1 then -1*z if z=-3 then product is 3 (prime) Insuff

2) z=1, taking above example.....

1*-2*2=-4 not a prime..you can try other numbers...it will always never be a prime..B has to be it...

I wish styolar was around..to verify.but i think B is the right

B is insuff

because 1 * 1 * 1 Not Prime
2 * 1 * 1 Prime
06 Feb 2007, 11:29
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