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Is 2(a+b-c) an odd integer? 1. a, b and c are consecutive

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Is 2(a+b-c) an odd integer? 1. a, b and c are consecutive [#permalink] New post 07 May 2010, 09:32
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

89% (02:18) correct 11% (01:49) wrong based on 5 sessions
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 07 May 2010, 10:21
ykaiim wrote:
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?


You forgot to multiply the -1 by 2

2(a+b-c)
2(0+1-2)
2(-1) = -2

or 2a + 2b - 2c
2(0) + 2(1) - 2(2)
2-4 = -2

Is the question correct? Multiplying anything by 2 will never give an odd so the question states the answer. In which case you wouldn't need to test 1 or 2
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 07 May 2010, 16:07
lagomez wrote:
ykaiim wrote:
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?


You forgot to multiply the -1 by 2

2(a+b-c)
2(0+1-2)
2(-1) = -2

or 2a + 2b - 2c
2(0) + 2(1) - 2(2)
2-4 = -2

Is the question correct? Multiplying anything by 2 will never give an odd so the question states the answer. In which case you wouldn't need to test 1 or 2


I agree with lagomez. any number x 2 = Even
Something must be wrong
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 07 May 2010, 17:11
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ykaiim wrote:
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?


2(a+b-c) can be:
odd, in case a+b-c=\frac{odd}{2};
even, in case a+b-c=integer
not an integer at all, in case a+b-c does not equal to any above. For example: a+b-c=\sqrt{2} or a+b-c=0.3.

Guess statement (1) is saying: "a, b and c are consecutive integers". The word "consecutive" is redundant here. Just knowing that "a, b and c are integers" is enough to say that this statement is sufficient to answer the question. And the answer would be NO: a, b and c are integers --> a+b-c=integer --> 2(a+b-c)=even.

Statement (2) is clearly not sufficient.
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 07 May 2010, 17:31
Bunuel wrote:
ykaiim wrote:
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?


2(a+b-c) can be:
odd, in case a+b-c=\frac{odd}{2};
even, in case a+b-c=integer
not an integer at all, in case a+b-c does not equal to any above. For example: a+b-c=\sqrt{2} or a+b-c=0.3.

Guess statement (1) is saying: "a, b and c are consecutive integers". The word "consecutive" is redundant here. Just knowing that "a, b and c are integers" is enough to say that this statement is sufficient to answer the question. And the answer would be NO: a, b and c are integers --> a+b-c=integer --> 2(a+b-c)=even.

Statement (2) is clearly not sufficient.


What numbers can be substituted for A, B, and C and when multiplied by 2 gives you an odd integer?
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 07 May 2010, 17:49
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lagomez wrote:
Bunuel wrote:
ykaiim wrote:
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?


2(a+b-c) can be:
odd, in case a+b-c=\frac{odd}{2};
even, in case a+b-c=integer
not an integer at all, in case a+b-c does not equal to any above. For example: a+b-c=\sqrt{2} or a+b-c=0.3.

Guess statement (1) is saying: "a, b and c are consecutive integers". The word "consecutive" is redundant here. Just knowing that "a, b and c are integers" is enough to say that this statement is sufficient to answer the question. And the answer would be NO: a, b and c are integers --> a+b-c=integer --> 2(a+b-c)=even.

Statement (2) is clearly not sufficient.


What numbers can be substituted for A, B, and C and when multiplied by 2 gives you an odd integer?


Note that stem does not say that a, b and c are integers.

So for example: a=3/2, b=0, c=0 --> 2(a+b-c)=3. As I said if a+b-c=\frac{odd}{2}, then 2(a+b-c)=2*\frac{odd}{2}=odd. This option is ruled out by statement (1), which says that a, b and c are integers.

Hope it's clear.
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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 07 May 2010, 21:13
Thanks Bunuel.

I think I need some revision also on Number Properties.
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 08 May 2010, 03:56
Bunuel wrote:
ykaiim wrote:
Is 2(a+b-c) an odd integer?

1. a, b and c are consecutive numbers
2. b=a+c

The OA is A. But, I think it is incorrect.
Case1: 0,1,2 the a+b-c = -1 (Yes)
Case2: 1,2,3 the a+b-c = 0 (No)

Can someone tell me where I am wrong?


2(a+b-c) can be:
odd, in case a+b-c=\frac{odd}{2};
even, in case a+b-c=integer
not an integer at all, in case a+b-c does not equal to any above. For example: a+b-c=\sqrt{2} or a+b-c=0.3.

Guess statement (1) is saying: "a, b and c are consecutive integers". The word "consecutive" is redundant here. Just knowing that "a, b and c are integers" is enough to say that this statement is sufficient to answer the question. And the answer would be NO: a, b and c are integers --> a+b-c=integer --> 2(a+b-c)=even.

Statement (2) is clearly not sufficient.

totally right
I assumed that a, b and c were integers
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Re: GmatClub Test: Number Properies - I (DS) [#permalink] New post 16 May 2010, 14:22
yup A must be the ans
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Re: Is 2(a+b-c) an odd integer? 1. a, b and c are consecutive [#permalink] New post 08 Nov 2013, 11:38
If we substitute b = a + c in 2(a+b-c), we get 4a. Now, whatever the value of a, the outcome will always be even. This statement should be sufficient too. In my opinion, the answer should be D.

I am not sure that whether what I have done is correct but, this is what came to my mind when I was attempting this question; I marked D.
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Re: Is 2(a+b-c) an odd integer? 1. a, b and c are consecutive [#permalink] New post 09 Nov 2013, 01:47
Expert's post
AasaanHai wrote:
If we substitute b = a + c in 2(a+b-c), we get 4a. Now, whatever the value of a, the outcome will always be even. This statement should be sufficient too. In my opinion, the answer should be D.

I am not sure that whether what I have done is correct but, this is what came to my mind when I was attempting this question; I marked D.


Please read the thread carefully:
is-2-a-b-c-an-odd-integer-1-a-b-and-c-are-consecutive-93832.html#p722067
is-2-a-b-c-an-odd-integer-1-a-b-and-c-are-consecutive-93832.html#p722073

The correct answer is A, not D.
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NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: Is 2(a+b-c) an odd integer? 1. a, b and c are consecutive   [#permalink] 09 Nov 2013, 01:47
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