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A question from Gmat prep

This topic has 4 member replies
banona Senior | Next Rank: 100 Posts Default Avatar
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A question from Gmat prep

Post Fri Mar 02, 2007 5:38 pm
I had the following DS question in my Gmatprep test. It's just confusing me as I don't think the answer is C.
The question says, x and y are integers, is x*(y+1) even ?

1- x and y are prime numbers
2 - x > 7

my answer was A, but Gmatprep said C

Did anybody encounter the same question ?

Thank you

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Vasudha Senior | Next Rank: 100 Posts Default Avatar
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Post Sun Mar 11, 2007 1:57 pm
So if you consider the first statement
"x and y are prime"
x(y+1)

for x=2 and y=3 , 2*4=Even
for x=3 and y=2, 3*3=Odd
Hence, insufficient

Second Statement "x>7" is insufficient coz x can be even making the product even or x and y can both be odd making the product odd.

Together Also
x=11,13....
y=2,3,5 etc

Hence for x=11 y=2, 11*3 = odd
for x=11 y=3, 11*4 =even

Hence the answer should be E

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Vasudha Senior | Next Rank: 100 Posts Default Avatar
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Post Sun Mar 11, 2007 1:45 pm
I did get this question when I took the practice test

Have u written "-x and y are prime numbers" and "-x>7"?
As far as I remember, the statements were "x and y are prime" and "x>7"

Moreover primes are always positive.

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Neo2000 Legendary Member
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Post Fri Mar 02, 2007 6:39 pm
Prime numbers are
2,3,5,7,11,

From 2
X at the very least has to be = 11
If y = 2
11*(2+1) = Odd
FOr anything else
It will beome Even

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jayhawk2001 Community Manager
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Post Sat Mar 03, 2007 10:10 am
I can't see how the answer can be C.

1 - Insufficient. As an example,
x = 3, y = 2 implies x(y+1) is odd
x = 2, y = 3 implies x(y+1) is even

2 - Insufficient. x can be even or odd

Combining 1 and 2, we can infer that x is odd.

If y is 2, x(y+1) is odd
If y is 3,5,7 ... x(y+1) is even

So, I'm inclined towards E.

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