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Am I over considering all possibilities?

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Am I over considering all possibilities?

by arpan307 » Fri Jun 24, 2011 7:02 pm
Q. A set of numbers has the property that for any number t in the set, t+2 is in the set. If -1 is in the set, which of the following must also be in the set?

I. -3
II 1
III. 5

(A) I only (B) II only (c) I and II only (D) II and III only (E) I, II and III

Okay people just tell me why can't -3 be there? since -1 is present, it acts as t+2 for some t right? now this t comes out to be -3.
The OA is D
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by MM_Ed » Fri Jun 24, 2011 7:19 pm
p: If t is in the set, t+2 is in the set.
q: If t+2 is in the set, t is in the set.

p does not imply q. You get 1 and 5 from p, but -3 from q. For all you know, -1 is the smallest number in the set : )
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by edvhou812 » Fri Jun 24, 2011 10:43 pm
MM_Ed wrote:p: If t is in the set, t+2 is in the set.
q: If t+2 is in the set, t is in the set.

p does not imply q. You get 1 and 5 from p, but -3 from q. For all you know, -1 is the smallest number in the set : )
And for all we know, -1 is just another number in the set. It is easy to find that 1 is in the set, but one needs to consider that the set is infinite in both directions on the number line, which is why we don't stop at 1. I rarely rant when I get the wrong answer, but this question is poorly written.
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by arpan307 » Sat Jun 25, 2011 12:03 am
edvhou812 wrote:
MM_Ed wrote:p: If t is in the set, t+2 is in the set.
q: If t+2 is in the set, t is in the set.

p does not imply q. You get 1 and 5 from p, but -3 from q. For all you know, -1 is the smallest number in the set : )
And for all we know, -1 is just another number in the set. It is easy to find that 1 is in the set, but one needs to consider that the set is infinite in both directions on the number line, which is why we don't stop at 1. I rarely rant when I get the wrong answer, but this question is poorly written.

Well people its an authentic question. source - Quantitave review, 2nd edition, no. 158
Can we have some expert comment please!!
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by winniethepooh » Sat Jun 25, 2011 12:34 am
Sorry, posted wrong answer.
The answer is D.
-1 is in the set, so the possibility of -3 cannot be determined.as -1 can be the first number.
So we add 2 to -1 = -1+2= 1,
we add 2 to 1 = 1+2= 3, and
we add another 2 to 3 = 3+2 = 5.
so the answer is, 1 and 5, both are possible!
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by arpan307 » Sat Jun 25, 2011 3:10 am
MM_Ed wrote:p: If t is in the set, t+2 is in the set.
q: If t+2 is in the set, t is in the set.

p does not imply q. You get 1 and 5 from p, but -3 from q. For all you know, -1 is the smallest number in the set : )
hi, i know we shouldn't assume anything in GMAT, but here's a doubt:

first of all its not mentioned its a finite set or that -1 is the first element of the said set.

Sorry people, could anyone please clarify. this problem is really bugging me.
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by winniethepooh » Sat Jun 25, 2011 3:57 am
In absence of any information you cant follow your own inferences.
The question in no way instructs you to calculate all the possibilities around -1. I do understand that if -1 is not the first element of the set then it would be a result of -3. But in the absence of information to the contrary assume it to be the first term(I am using the word assume).

If the question had provided you the information that -1 is an element from somewhere in the middle of the set then your argument would have been valid.
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