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# Triskaidekaphobia! - m13, Q. 13

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Manager
Joined: 11 Jul 2010
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Triskaidekaphobia! - m13, Q. 13 [#permalink]

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30 Oct 2010, 03:15
Is (x - y)*(x + y) an even integer?

1. x and y are integers
2. [x + y] is even

[Reveal] Spoiler:
Ans = C Query: Whats wrong with B? Only integers can be "even" - so x+y is an Even Integer per Stem 2... can x-y ever be a non integer if x+y is an integer?
Manager
Joined: 03 Sep 2010
Posts: 75
Location: Israel
GMAT 1: 660 Q47 V34
GMAT 2: 670 Q48 V34
GPA: 3.2
WE: Operations (Non-Profit and Government)
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Kudos [?]: 31 [0], given: 2

Re: Triskaidekaphobia! - m13, Q. 13 [#permalink]

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30 Oct 2010, 06:15

(1) - Insufficient. Lets plug in. X=5, Y=2. (5-2)*(5+2)=21, X=4, Y=2, (4+2)*(4-2)=12. Thus BCE.
(2) Insufficient. Let plug in: X=1.3, Y=0.7. (1.3+0.7)*(1.3-0.7)=1.2 (X+Y is even, like is said in the statement). Thus CE

If taken together - Lets plug in X=3 Y=1 , (3+1)*(3-1)=8, X=4 Y=2, (4-2)*(4+2)=12. Sufficient!
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Re: Triskaidekaphobia! - m13, Q. 13 [#permalink]

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30 Oct 2010, 06:41
Expert's post
gmat1011 wrote:
Is (x - y)*(x + y) an even integer?

1. x and y are integers
2. [x + y] is even

[Reveal] Spoiler:
Ans = C Query: Whats wrong with B? Only integers can be "even" - so x+y is an Even Integer per Stem 2... can x-y ever be a non integer if x+y is an integer?

Answer is C because if x and y are not integers (second statement does not state that), then x+y may be even (statement 2) and (x-y)*(x+y) may not be an integer at all.

Example:
x=1.8 and y=0.2 - answer to the question NO.
x=1.5 and y=0.5 - answer to the question YES.

Statement (1) says that x and y are integers so combined statements guarantee (x-y)*(x+y) being even.

Hope it helps.
_________________
Re: Triskaidekaphobia! - m13, Q. 13   [#permalink] 30 Oct 2010, 06:41
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# Triskaidekaphobia! - m13, Q. 13

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