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m04 Q23

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m04 Q23 [#permalink] New post 14 Sep 2008, 06:12
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Question Stats:

75% (01:27) correct 24% (00:17) wrong based on 2 sessions
Is integer Z odd?

1. \frac{Z}{3} is odd
2. 3Z is odd

[Reveal] Spoiler: OA
D

Source: GMAT Club Tests - hardest GMAT questions

Here OA is D with explanation S2 also implies that Z is odd.

Why can't S2 be a fraction? For example 5/3.

I think answer to this question needs to be changed.
[Reveal] Spoiler: OA
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Re: m04 Q23 [#permalink] New post 14 Sep 2008, 06:48
I'm not sure why you're saying "Why can't statement 2 be a fraction?" when the question stem says "integer Z".

if \frac{Z}{3} is odd, then this means the result is an integer because decimials are neither even nor odd. If we take values for Z that when divided by 3 give us integers, we can use (3, 6, 9, 12, 15, 18, 21...}

The resulting value when each is divided by 3 is {1, 2, 3, 4, 5, 6, 7...}. Lets look at which values for Z give us the odd value...that would be 3, 9, 15, 21..etc. These are also odd. So Z is odd from statement 1.

With statement 2, we have to remember number properties. Odd * Odd = Odd [always!]. So if 3*Z is odd, Z must be odd. Just as simple as that.

vishy007 wrote:
Is integer Z odd?

1. \frac{Z}{3} is odd
2. 3Z is odd

Here OA is D with explanation S2 also implies that Z is odd.

Why can't S2 be a fraction? For example 5/3.

I think answer to this question needs to be changed.

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Re: m04 Q23 [#permalink] New post 14 Sep 2008, 09:25
Oops sorry... I have missed an obvious point in question stem.

Thanks for correcting.
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Re: m04 Q23 [#permalink] New post 14 Oct 2010, 19:43
D. odd*odd=odd
3 is odd
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Re: m04 Q23 [#permalink] New post 18 Oct 2012, 05:18
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vishy007 wrote:
Is integer Z odd?

1. \frac{Z}{3} is odd
2. 3Z is odd

[Reveal] Spoiler: OA
D

Source: GMAT Club Tests - hardest GMAT questions

Here OA is D with explanation S2 also implies that Z is odd.

Why can't S2 be a fraction? For example 5/3.

I think answer to this question needs to be changed.


Is integer z odd?

(1) \frac{z}{3} is odd --> \frac{z}{3}=odd --> z=3*odd=odd. Sufficient.
(2) 3z is odd --> 3z=odd --> in order the product of two integers 3 and z to be odd both must be odd. So, z=odd. Sufficient.

Answer: D.
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Re: m04 Q23 [#permalink] New post 18 Oct 2012, 05:23
The email that comes as GMAT question of the day, says -- 2. 49 is odd. This seemed odd, but looking at the actuals question on this webpage makes it clear about answer being D.
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Re: m04 Q23 [#permalink] New post 18 Oct 2012, 05:30
(i) z/3=odd
z=oddx3
z=oddXodd
always odd-sufficient

(ii) 3z=odd
if z is odd then 3z is odd, if z is even then 3z is even - sufficient

Answer :D
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Re: m04 Q23 [#permalink] New post 18 Oct 2012, 07:43
Went for A when I received it as question of the day since 2. 49 is odd seemed quite irrelevant to solve the question. But when I saw the actual question I knew it had to be D
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Re: m04 Q23 [#permalink] New post 18 Oct 2012, 11:42
Here we go:
z/3 is odd, hence z is odd, it could be 3 or any odd number multiplied by 3. - keep A
3*z - is odd, it could be look above, hence the answer is (D) each answer choices is sufficient. Did not delve deep since it is data sufficiency quesiton
Correct me, if I went awry.






vishy007 wrote:
Is integer Z odd?

1. \frac{Z}{3} is odd
2. 3Z is odd

[Reveal] Spoiler: OA
D

Source: GMAT Club Tests - hardest GMAT questions

Here OA is D with explanation S2 also implies that Z is odd.

Why can't S2 be a fraction? For example 5/3.

I think answer to this question needs to be changed.

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Re: m04 Q23 [#permalink] New post 19 Oct 2012, 12:50
I concur. Both the options 1 & 2 are based on the rule odd * odd = odd. Kind of easy to crack.
Re: m04 Q23   [#permalink] 19 Oct 2012, 12:50
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