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# Q10: A set of numbers has the property that for any number t

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Manager
Joined: 11 Jan 2007
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Q10: A set of numbers has the property that for any number t [#permalink]

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04 Jul 2007, 20:56
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Q10:
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
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cool

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VP
Joined: 10 Jun 2007
Posts: 1434

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Re: the number of property [#permalink]

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04 Jul 2007, 21:37
jet1445 wrote:
Q10:
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

C.

If t = -1, t+2 = 1
if t+2 = -1, t = -3

OA?

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VP
Joined: 07 Nov 2005
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04 Jul 2007, 22:10
Yes should be D.
-1 could be the first element.
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Trying hard to conquer Quant.

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Director
Joined: 09 Aug 2006
Posts: 754

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Re: the number of property [#permalink]

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04 Jul 2007, 23:52
jet1445 wrote:
Q10:
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

D.
-1 is in the set only means that -1+2= 1 is in the set, which also means that 1+2=3 is also in the set.
-3 does not have to be in the set since the first number in the set could be -1.

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CIO
Joined: 09 Mar 2003
Posts: 461

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Re: the number of property [#permalink]

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05 Jul 2007, 05:27
jet1445 wrote:
Q10:
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

I go with D, for the same reasons above.

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Director
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Posts: 548

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05 Jul 2007, 08:23
Why it cant be E. Why are you assuming that -1 is the first member in the set ? My unanimous choice was E. Am is wrong here ?

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CIO
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05 Jul 2007, 08:28
trahul4 wrote:
Why it cant be E. Why are you assuming that -1 is the first member in the set ? My unanimous choice was E. Am is wrong here ?

Because the question says, "which of the following MUST be in the set"

We only know for a fact that if a number is in the set, so is 2 plus that number. But that doesn't imply that the number is in the set BECAUSE of a previous number.

We know -1 is there. It implies that 1 is there, which pushes us to 3, which pushes us to 5. Those are "MUSTS". But it doesn't mean that -3 MUST be there.

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05 Jul 2007, 08:28
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