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gmatclub DS problem

by arora007 » Tue Jul 06, 2010 7:01 am
Is A + B + C even?

1. A - C - B is even
2. (A - C)/B is odd


OA is E

gmatclub math problem
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by kvcpk » Tue Jul 06, 2010 7:13 am
Is A + B + C even?

1. A - C - B is even
let A=B=C=0
A+B+C is even
let a=1, b=c=0
A+B+C is odd
INSUFF
2. (A - C)/B is odd
Let (A-C)/B =2k+1
A-C = 2kB+B
B+C = A-2kB
A+B+C=2A-2KB
=2(A-KB)
This is always even

I believe answer should be B

Am i missing something?
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by Rich@VeritasPrep » Tue Jul 06, 2010 7:56 am
Hey kvcpk,

The tricky thing here is that A, B, and C are not specified as integers.

So, while you showed that A+B+C = 2(A-KB) , we don't know that A and B are integers, so we can't say for sure that the right side of the equation is even.

If A = 2, B = 1, and C = 1, then the conditions of both statements are met, and A+B+C is even.

However, if A = 3/2, B = 1/2, and C = 1, the conditions of both statements are still met, but A+B+C is odd.

Thus the final answer is E
Rich Zwelling
GMAT Instructor, Veritas Prep
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by kvcpk » Tue Jul 06, 2010 8:57 am
raz1024 wrote:Hey kvcpk,

The tricky thing here is that A, B, and C are not specified as integers.

So, while you showed that A+B+C = 2(A-KB) , we don't know that A and B are integers, so we can't say for sure that the right side of the equation is even.

If A = 2, B = 1, and C = 1, then the conditions of both statements are met, and A+B+C is even.

However, if A = 3/2, B = 1/2, and C = 1, the conditions of both statements are still met, but A+B+C is odd.

Thus the final answer is E
oh.. thanks Raz.. missed that..
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by nikhilkatira » Fri Jul 09, 2010 10:10 am
kvcpk wrote:
raz1024 wrote:Hey kvcpk,

The tricky thing here is that A, B, and C are not specified as integers.

So, while you showed that A+B+C = 2(A-KB) , we don't know that A and B are integers, so we can't say for sure that the right side of the equation is even.

If A = 2, B = 1, and C = 1, then the conditions of both statements are met, and A+B+C is even.

However, if A = 3/2, B = 1/2, and C = 1, the conditions of both statements are still met, but A+B+C is odd.

Thus the final answer is E
oh.. thanks Raz.. missed that..

Hey raz1024

what approach should be used for guessing such problem ? ( if trail and error doesn't work )
Best,
Nikhil H. Katira
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