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Source: — Data Sufficiency |
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by arvindm07 » Thu Aug 07, 2008 9:46 am
1) x(y+5) is even - x can be even or odd if (y+5) is even, we donot know of (y+5) so INSUFFICIENT.

2) 6y^2 + 41y + 25 is even - tells us only about y so INSUFFICIENT.

Together:
from 2) y(6y+41) + 25 = even implies that y(6y+41) is odd since 25 is odd and only odd + odd = even. Further, both y and (6y+41) have to be odd for the product to be odd and that says that y is odd.
Now plugging Odd number y into 1) gives (y+5) as even and hence x can be either even or odd.
Both together is insufficient.

Hence, E
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by bha » Thu Aug 07, 2008 10:40 am
arvindm07 wrote:1) x(y+5) is even - x can be even or odd if (y+5) is even, we donot know of (y+5) so INSUFFICIENT.

2) 6y^2 + 41y + 25 is even - tells us only about y so INSUFFICIENT.

Together:
from 2) y(6y+41) + 25 = even implies that y(6y+41) is odd since 25 is odd and only odd + odd = even. Further, both y and (6y+41) have to be odd for the product to be odd and that says that y is odd.
Now plugging Odd number y into 1) gives (y+5) as even and hence x can be either even or odd.
Both together is insufficient.

Hence, E
Hmm..I am getting 'C'.Can anyone let me know, where I am going wrong?
using stmt 2,
6Y^2+41Y+25 = even
25 is odd
6Y^2 is even (even*anything is even)
So
even+41y+odd = even
odd+41y=even (as even+odd= odd)
hence 41y has to be odd (as odd + odd = even)
41Y= even
so y has to even (odd * even = even and odd * odd cannot be even)
now using this in stmt1,
x(even+5) = even
x*odd = even
hence x has to be even...
Hence answer is 'C'.
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by Stuart@KaplanGMAT » Thu Aug 07, 2008 11:00 am
bha wrote:hence 41y has to be odd (as odd + odd = even)
41Y= even
so y has to even (odd * even = even and odd * odd cannot be even)
Here's your problem: first you say 41y has to be odd (which is correct), then in the next line you say "41Y=even", contradicting yourself.

41Y = odd, so Y must be odd.
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by bha » Thu Aug 07, 2008 11:38 am
Stuart Kovinsky wrote:
bha wrote:hence 41y has to be odd (as odd + odd = even)
41Y= even
so y has to even (odd * even = even and odd * odd cannot be even)
Here's your problem: first you say 41y has to be odd (which is correct), then in the next line you say "41Y=even", contradicting yourself.

41Y = odd, so Y must be odd.
My bad :oops: ..thanks for correcting me...
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