^^ this is the exact rationale. This problem has 2 main components. 1) It's an infinite set always increasing by 2, and 2) You can only assume that -1 is the lowest number since it's a MUST question. Starting with -1 yields the narrowest choice, and D is thus, as egybs said, unambiguously correct.egybs wrote:Wow.. blast from the past! As I said a year and a half ago, before I scored 99th percentile on the gmat, the answer is unambiguously D. In case the old posts are enough of an explanation here it goes again:
The set is going to be infinitely long and will continue increasing positively. Any number that's in the set will also have the same number + 2 (t+2). So if we know that 4 is in the set, 6, 8, 10,12, 14, 16, 18,20, etc, etc, etc are also definitely there.
So if we know that -1 is in the set, we know with certainty that 1,3,5,7,etc are also in the set.
What we don't know is where the trend starts. -1 could be the lowest number, but it could also be -3, or -5, or even -4.. we just don't know where it starts. Therefore, the only thing we can conclude with certainty is that -1,1,3,5,7,9, etc are in the set. So the answer is, once again, unambiguously, D.
Set of Numbers
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lunarpower
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with statements like this one, it can actually help to take the variables out of the statement and express the statement purely in WORDS.
you can take any number that is there, ADD 2 to it, and the result will also be there.
in other words, you can always go UP by 2.
in particular, note that this statement does not work the other way around -- there is no evidence here that you can subtract 2 from any numbers that you might have.
the only number that we know we have, at the beginning, is -1. therefore, any number that we can get by starting with -1 and ADDING 2 at a time is all good.
should be (d).
in words:duke wrote:A set of numbers has the property that for any number t in the set, t + 2 is in the set.
you can take any number that is there, ADD 2 to it, and the result will also be there.
in other words, you can always go UP by 2.
in particular, note that this statement does not work the other way around -- there is no evidence here that you can subtract 2 from any numbers that you might have.
the only number that we know we have, at the beginning, is -1. therefore, any number that we can get by starting with -1 and ADDING 2 at a time is all good.
nope. you'd have to subtract to get this number.I. -3
these are all good.II. 1
III. 5
should be (d).
Ron has been teaching various standardized tests for 20 years.
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Quand on se sent bien dans un vêtement, tout peut arriver. Un bon vêtement, c'est un passeport pour le bonheur.
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akshitamadhan
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