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For a certain set of numbers, if x is in the set, then x - 3 [#permalink]
30 Jul 2012, 06:45

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65% (01:40) correct
35% (00:52) wrong based on 153 sessions

For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4 b) -1 c) -5

A. a only, B. b only, C. c only, D. a and b only E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer )

Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink]
30 Jul 2012, 07:02

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This post received KUDOS

Expert's post

jayoptimist wrote:

For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4 b) -1 c) -5

A. a only, B. b only, C. c only, D. a and b only E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer )

Notice that the question asks which of the following MUST be in the set, not COULD be in the set.

Since 1 is in the set, then so must be 1-3=-2. Similarly, since -2 is in the set, then so must be -2-3=-5. Could 4 and -1 be in the set? Certainly, but we don't know that for sure.

Answer: C.

Regarding your question: we don't know which is the source integer in the set, if it's 1, then 4 won't be in the set but if the source integer is say 7, then 4 will be in the set. So, 4 may or may not be in the set.

For a certain set of numbers, if x is in the set, x-3 is als [#permalink]
30 Dec 2012, 16:22

For a certain set of numbers, if x is in the set, x-3 is also in the set. If the number 1 is in the set, which of the following must also be in the set I) 4 II) -1 III) -5

the answer is III only, means -5.

They are reasoning that, 1 in the set, so -2 also in the set, so -5 also in the set, so -8 also in the set.

I wonder why 4 can't be in the set??? let consider 1 is x-3, not x, hence x = 4. What is the trap of GMAT here?

Re: For a certain set of numbers, if x is in the set, x-3 is als [#permalink]
30 Dec 2012, 20:40

1

This post received KUDOS

akhandamandala wrote:

For a certain set of numbers, if x is in the set, x-3 is also in the set. If the number 1 is in the set, which of the following must also be in the set I) 4 II) -1 III) -5

the answer is III only, means -5.

They are reasoning that, 1 in the set, so -2 also in the set, so -5 also in the set, so -8 also in the set.

I wonder why 4 can't be in the set??? let consider 1 is x-3, not x, hence x = 4. What is the trap of GMAT here?

(I always have problem with the trap of gmat)

We can look at this as a cause and effect problem. "x" is the cause and "x-3" is the effect. i.e. We are given that is "x" is in the set "x-3" is also in the set. The reverse need not necessarily be true. We cannot take the effect to be the cause.

_________________

Did you find this post helpful?... Please let me know through the Kudos button.

Re: For a certain set of numbers, if x is in the set, x-3 is als [#permalink]
31 Dec 2012, 02:06

Expert's post

akhandamandala wrote:

For a certain set of numbers, if x is in the set, x-3 is also in the set. If the number 1 is in the set, which of the following must also be in the set I) 4 II) -1 III) -5

the answer is III only, means -5.

They are reasoning that, 1 in the set, so -2 also in the set, so -5 also in the set, so -8 also in the set.

I wonder why 4 can't be in the set??? let consider 1 is x-3, not x, hence x = 4. What is the trap of GMAT here?

(I always have problem with the trap of gmat)

Merging similar topics. Please refer to the solutions above.

Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink]
31 Dec 2012, 11:21

2

This post received KUDOS

jayoptimist wrote:

For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4 b) -1 c) -5

A. a only, B. b only, C. c only, D. a and b only E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer )

I call them Verbal diaorea of GMAT. You have to follow these verbal vomits carefully. When they say x-3 is there only x-3 is guaranteed to be there nothing else. And so here you can not travel to the side of the stream.

Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink]
31 Dec 2012, 16:56

maibhihun wrote:

jayoptimist wrote:

For a certain set of numbers, if x is in the set, then x - 3 is also in the set. If the number 1 is in the set , which of the following must also be in the set ?

a) 4 b) -1 c) -5

A. a only, B. b only, C. c only, D. a and b only E. b and c only

I need to know why can't x-3 = 1 be considered? if yes then x = 4 (which is not the answer )

I call them Verbal diaorea of GMAT. You have to follow these verbal vomits carefully. When they say x-3 is there only x-3 is guaranteed to be there nothing else. And so here you can not travel to the side of the stream.

that's true, I have no problem with math, but I have quite problem with those kinds of "Verbal diaorea of GMAT". Hope exercises will help much. Thanks

Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink]
03 Mar 2014, 11:47

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Re: For a certain set of numbers, if x is in the set, then x - 3 [#permalink]
27 Apr 2014, 08:18

It does not make logical sense to only have -5 and 4 is not the correct answer.

Can't we take that 1 is the result of X -3 ? In which case, X = 4.

I cant agree with -5 more because it is one more "jump"

X = 1 .... 2nd number is ( -2 ) is fine with me. But the question did not say that "X - 6" also exists? Because X is still 1, and did not "move on" to become -2.

Agree its a bit of a "throw you off if you did not buy our official guide" even if you had maths as your bach degree.

Hope this kind of stuff don't pop up for my coming exam, but it cant be helped =)

gmatclubot

Re: For a certain set of numbers, if x is in the set, then x - 3
[#permalink]
27 Apr 2014, 08:18