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

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

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New post 26 Dec 2016, 18:06
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A
B
C
D
E

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  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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Re: If a and b are integers, is ab an odd?  [#permalink]

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New post 26 Dec 2016, 21:09
i think it should be A.. i have no clue how D..
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Re: If a and b are integers, is ab an odd?  [#permalink]

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New post 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

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Re: If a and b are integers, is ab an odd?  [#permalink]

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New post 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
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Re: If a and b are integers, is ab an odd?  [#permalink]

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New post 16 Jul 2017, 11:26
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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

Hence, Answer is D

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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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