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# The positive integers r, s, and t are such that r is

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Intern
Joined: 22 Jun 2010
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The positive integers r, s, and t are such that r is [#permalink]

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28 Jul 2010, 02:01
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85% (hard)

Question Stats:

49% (02:26) correct 51% (01:28) wrong based on 327 sessions

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The positive integers r, s, and t are such that r is divisible by s and s is divisible by t. Is r even?

(1) st is odd.
(2) rt is even.
[Reveal] Spoiler: OA
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Joined: 02 Sep 2009
Posts: 39622

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28 Jul 2010, 02:22
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mehdiov wrote:
The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even.

(1) $$st=odd$$, clearly not sufficient as no info about $$r$$, for example if $$r=6$$, $$s=1$$ and $$t=1$$ then answer is YES but if $$r=3$$, $$s=1$$ and $$t=1$$ then the answer is NO.

(2) $$rt=even$$. For product of 2 integers to be even either one or both must be even. Can $$r$$ not to be even? The only chance would be if $$t$$ is even and $$r$$ is odd. Let's check if this scenario is possible: if $$t$$ is even, so must be $$s$$, as $$s$$ is divisible by $$t$$ (if an integer is divisible by even it's even too). Now, if $$s$$ is even so must be $$r$$ by the very same reasoning. So scenario when $$r$$ is not even is not possible --> $$r=even$$. Sufficient.

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28 Jul 2010, 02:37
Bunuel wrote:
mehdiov wrote:
The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even.

(1) $$st=odd$$, clearly not sufficient as no info about $$r$$, for example if $$r=6$$, $$s=1$$ and $$t=1$$ then answer is YES but if $$r=3$$, $$s=1$$ and $$t=1$$ then the answer is NO.

(2) $$rt=even$$. For product of 2 integers to be even either one or both must be even. Can $$r$$ not to be even? The only chance would be if $$t$$ is even and $$r$$ is odd. Let's check if this scenario is possible: if $$t$$ is even, so must be $$s$$, as $$s$$ is divisible by $$t$$ (if an integer is divisible by even it's even too). Now, if $$s$$ is even so must be $$r$$ by the very same reasoning. So scenario when $$r$$ is not even is not possible --> $$r=even$$. Sufficient.

many thanks looks easy after the explanation

Do you have an idea about the level of this question ?
Math Expert
Joined: 02 Sep 2009
Posts: 39622

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28 Jul 2010, 02:44
mehdiov wrote:
Bunuel wrote:
mehdiov wrote:
The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even.

(1) $$st=odd$$, clearly not sufficient as no info about $$r$$, for example if $$r=6$$, $$s=1$$ and $$t=1$$ then answer is YES but if $$r=3$$, $$s=1$$ and $$t=1$$ then the answer is NO.

(2) $$rt=even$$. For product of 2 integers to be even either one or both must be even. Can $$r$$ not to be even? The only chance would be if $$t$$ is even and $$r$$ is odd. Let's check if this scenario is possible: if $$t$$ is even, so must be $$s$$, as $$s$$ is divisible by $$t$$ (if an integer is divisible by even it's even too). Now, if $$s$$ is even so must be $$r$$ by the very same reasoning. So scenario when $$r$$ is not even is not possible --> $$r=even$$. Sufficient.

many thanks looks easy after the explanation

Do you have an idea about the level of this question ?

Not very hard (600+) but tricky, as it's C-trap question: the question which is obviously sufficient if we take statements together. When we see such questions we should become very suspicious.
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07 Aug 2010, 03:44
Not very hard (600+) but tricky, as it's C-trap question: the question which is obviously sufficient if we take statements together. When we see such questions we should become very suspicious.[/quote]

what is C-trap?
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Manager
Joined: 24 Apr 2010
Posts: 62

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07 Aug 2010, 05:47
Bunuel wrote:

(1) $$st=odd$$, clearly not sufficient as no info about $$r$$, for example if $$r=6$$, $$s=1$$ and $$t=1$$ then answer is YES but if $$r=3$$, $$s=1$$ and $$t=1$$ then the answer is NO.

thanks...i was able to get to B but may be in 3 minutes.....
i complicated the question thinking like 2 4 8 and not thinking infact one can be one number or 2 numbers can be same 8 2 2 and so on...
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Joined: 10 Mar 2014
Posts: 245

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27 Apr 2014, 03:01
Bunuel wrote:
mehdiov wrote:
The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even.

(1) $$st=odd$$, clearly not sufficient as no info about $$r$$, for example if $$r=6$$, $$s=1$$ and $$t=1$$ then answer is YES but if $$r=3$$, $$s=1$$ and $$t=1$$ then the answer is NO.

(2) $$rt=even$$. For product of 2 integers to be even either one or both must be even. Can $$r$$ not to be even? The only chance would be if $$t$$ is even and $$r$$ is odd. Let's check if this scenario is possible: if $$t$$ is even, so must be $$s$$, as $$s$$ is divisible by $$t$$ (if an integer is divisible by even it's even too). Now, if $$s$$ is even so must be $$r$$ by the very same reasoning. So scenario when $$r$$ is not even is not possible --> $$r=even$$. Sufficient.

HI Bunnel,

I have a doubt on this.

Generally we treat both the statements as seprate statements. then why are you mixing them.

If I will go with st2 i can r can be even or odd because rt = even ( r and t both can be even or one of them is even) now if we refer even to r and t then st1 will contradict.

is this the reason you are not considering both r and t as even?

Thanks.
Math Expert
Joined: 02 Sep 2009
Posts: 39622

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28 Apr 2014, 02:27
PathFinder007 wrote:
Bunuel wrote:
mehdiov wrote:
The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even.

(1) $$st=odd$$, clearly not sufficient as no info about $$r$$, for example if $$r=6$$, $$s=1$$ and $$t=1$$ then answer is YES but if $$r=3$$, $$s=1$$ and $$t=1$$ then the answer is NO.

(2) $$rt=even$$. For product of 2 integers to be even either one or both must be even. Can $$r$$ not to be even? The only chance would be if $$t$$ is even and $$r$$ is odd. Let's check if this scenario is possible: if $$t$$ is even, so must be $$s$$, as $$s$$ is divisible by $$t$$ (if an integer is divisible by even it's even too). Now, if $$s$$ is even so must be $$r$$ by the very same reasoning. So scenario when $$r$$ is not even is not possible --> $$r=even$$. Sufficient.

HI Bunnel,

I have a doubt on this.

Generally we treat both the statements as seprate statements. then why are you mixing them.

If I will go with st2 i can r can be even or odd because rt = even ( r and t both can be even or one of them is even) now if we refer even to r and t then st1 will contradict.

is this the reason you are not considering both r and t as even?

Thanks.

The statements do not contradict: st is odd and rt is even is possible when r is even and both s and t are odd.
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Re: The positive integers r, s, and t are such that r is [#permalink]

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02 Jun 2016, 12:25
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: The positive integers r, s, and t are such that r is [#permalink]

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23 Jun 2017, 03:12
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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Re: The positive integers r, s, and t are such that r is [#permalink]

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23 Jun 2017, 07:04
This is how I solved it:

Is r even?

r is divisible by s, hence r = ns
s is divisible by t, hence s = mt
combining, r = nmt

1-> st = odd. This implies, both s and t are odd. no impact on r. insuff.
2 -> rt = even
Hence, r = even or t = even or both = even
If t = even, then r = nmt = even
If r = odd, then r is even for rt = even
Suff.
Re: The positive integers r, s, and t are such that r is   [#permalink] 23 Jun 2017, 07:04
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# The positive integers r, s, and t are such that r is

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