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If x and y are integers, is the value of x(y + 1) even?

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Director
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If x and y are integers, is the value of x(y + 1) even? [#permalink] New post 16 Mar 2013, 02:52
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If x and y are integers, is the value of x(y + 1) even?

(1) x and y are prime numbers.
(2) y > 7

[Reveal] Spoiler:
Why is the answer C I'm getting E aren't there multiple cases when the statements are combined?
[Reveal] Spoiler: OA

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Last edited by Bunuel on 16 Mar 2013, 02:56, edited 1 time in total.
Edited the question.
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Re: If x and y are integers, is the value of x(y + 1) even? [#permalink] New post 16 Mar 2013, 03:02
Expert's post
fozzzy wrote:
If x and y are integers, is the value of x(y + 1) even?

(1) x and y are prime numbers.
(2) y > 7

Why is the answer C I'm getting E aren't there multiple cases when the statements are combined?


Please hide OA under the spoiler.

If x and y are integers, is the value of x(y + 1) even?

x(y + 1) will be even if x is even or/and y is odd.

(1) x and y are prime numbers. If x is ANY odd prime and y is an even prime, so 2, then x(y + 1) = odd*(even+1) = odd*odd=odd but in all other cases x(y + 1) = even. Not sufficient.

(2) y > 7. Clearly insufficient.

(1)+(2) Since y = prime > 7, then y = odd, thus x(y + 1) = x(odd + 1) = x*even = even. Sufficient.

Answer: C.

Hope it's clear.
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Kudos [?]: 251 [0], given: 543

Re: If x and y are integers, is the value of x(y + 1) even? [#permalink] New post 16 Mar 2013, 05:27
Thanks missed the prime part silly error. I don't know how to insert the second spoiler... I'll do that next time around.
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Kudos [?]: 250 [0], given: 67

Re: If x and y are integers, is the value of x(y + 1) even? [#permalink] New post 16 Mar 2013, 05:36
fozzzy wrote:
Thanks missed the prime part silly error. I don't know how to insert the second spoiler... I'll do that next time around.


Hey
One quick point here all primes except 2, when 1 is added will give an even number.
Statement provides a clue for the above, So when it is greater than 7 the constraint of 2 is avoided.....and hence the answer is C

Consider Kudos if my post helps.

Archit
Re: If x and y are integers, is the value of x(y + 1) even?   [#permalink] 16 Mar 2013, 05:36
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