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is ans is correct????

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is ans is correct????

by arorag » Mon Sep 01, 2008 11:22 am
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


Ans D
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Re: is ans is correct????

by sudhir3127 » Mon Sep 01, 2008 11:50 am
arorag wrote: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


Ans D
i will go with D as well

it tells us that for every t t+2 will be there ,..
so be the set contains -1

-1 (+2 ) on a number line will be +1
and u will also have 3 ,5,7...............

there is a chance u may or may not have -3

this is a trap answer...

"we can say -3 is there that the reason -1 is there" which is logically correct and holds good according to the Question... but what if

the set starts from -1 ..then we wont have -3... so its a trap answer...

hope this helps...
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by sushilmore » Mon Sep 01, 2008 2:57 pm
Hi Sudhir,

They have not mentioned that set starts from -1. It just mentions that -1 is part of the set. So I think -3 should be part of the set and hence E
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Answer is E

by GMAT Genie » Mon Sep 01, 2008 11:34 pm
i will go with E as -3 can be in the set and there is no starting point of the set
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Answer is E

by GMAT Genie » Mon Sep 01, 2008 11:36 pm
i will go with E as -3 can be in the set and there is no starting point of the set
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by Ian Stewart » Tue Sep 02, 2008 3:11 am
-3 certainly can be in the set, but that's not what the question asks. The question asks whether -3 must be in the set. And -3 does not need to be in the set; the set could be:

{-1, 1, 3, 5, 7, ...}

Then if you pick any number t in the set, t+2 is also in the set, so this set satisfies the conditions given in the question. The answer is D.
Last edited by Ian Stewart on Tue Sep 02, 2008 5:56 pm, edited 1 time in total.
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by GMAT Genie » Tue Sep 02, 2008 4:14 pm
My understanding is that if there is t in the set, then t+2 must be in the set.
Since the question is saying that -1 is in the set, that means the -3 is definitley present in the set to allow -1 in the set. I may be wrong but thats my interpretation
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by GMAT Genie » Tue Sep 02, 2008 4:24 pm
I again read the question and I conclude that D is more appropriate. The trick in the question is may be and must be. Answer D is more appropriate for 'Must be' part of the question
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