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# If a and b are integers, is ab an odd?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7252
GMAT 1: 760 Q51 V42
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If a and b are integers, is ab an odd?  [#permalink]

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26 Dec 2016, 18:06
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Difficulty:

25% (medium)

Question Stats:

72% (01:07) correct 28% (01:13) wrong based on 74 sessions

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If a and b are integers, is ab an odd?

1) a=0
2) b=1-a

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $149 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Intern Joined: 11 Dec 2016 Posts: 4 Re: If a and b are integers, is ab an odd? [#permalink] ### Show Tags 26 Dec 2016, 21:09 i think it should be A.. i have no clue how D.. Intern Joined: 04 Mar 2016 Posts: 45 Location: India Re: If a and b are integers, is ab an odd? [#permalink] ### Show Tags 27 Dec 2016, 00:10 1 1) a = 0 . Clearly sufficient.. since product will be 0. Answer is NO. 2) A Bit Tricky but Sufficient, will put forth a few secenarios B= 0 A= -1... AB = 0 NO B= 1 A= 0 ... AB= 0 N0 B= 2 A= 1...AB= 2...NO In short , it will be multiplication of odd and even integer which will always be even, either consecutive (if on Positive Side) or consecutive by absolute value. If A= 90, B=-89... AB= -8010... So answer is NO... This sufficient Answer is D Omkar Kamat When The Going Gets Tough, The Tough Gets Going !! Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7252 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If a and b are integers, is ab an odd? [#permalink] ### Show Tags 31 Dec 2016, 01:43 ==> In the original condition, there are 2 variables (a, b), and therefore C is most likely to be the answer. By solving con 1) and con 2), from a=0 and b=1, you get ab0*1=0=even, hence no, it is sufficient. Therefore, C is the answer. However, this is an integer question, one of the key questions. Thus, if you apply CMT 4 (A, B), if 1) a=0, you get ab=0 and it is always even, hence no, it is sufficient. Also, for con 2), from a+b=1=odd, and (a, b)=(odd, even), (even, odd), you get ab=even, hence yes, it is sufficient. Therefore, the answer is D. This question is related to CMT 4(B). In other words, con 1) is easy and con 2) is difficult, so you apply CMT 4(B) (If you get A and B easily, consider B). Answer: D _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$149 for 3 month Online Course"
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Re: If a and b are integers, is ab an odd?  [#permalink]

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16 Jul 2017, 11:26
1
If a and b are integers, is ab an odd?

1) $$a=0$$

As $$a = 0$$, for any value of b and product, $$a * b$$ will always be ZERO

As we know that ZERO is EVEN, the answer the question is ab an odd? is NO

Hence, (1) ===== is SUFFICIENT

2) $$b=1-a$$

As $$b=1-a$$, we know that either a and b will be ODD or EVEN or vice a versa.

And, as ODD * EVEN = EVEN

the answer the question is ab an odd? is NO

Hence, (2) ===== is SUFFICIENT

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Re: If a and b are integers, is ab an odd?   [#permalink] 16 Jul 2017, 11:26
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