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Source: — Data Sufficiency |
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by yellowho » Sun Jan 23, 2011 10:31 pm
D?

[quote="Night reader"]The set S of numbers has the following properties:

i) If x is in S, then 1/x is in S.
ii) If both x and y are in S, then so is x+y

Is 3 in S?

(1) 1/3 is in S
(2) 1 is in S[/quote]
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by gmatusa2010 » Sun Jan 23, 2011 11:15 pm
D looks fine. Whats the OA here?
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by Geva@EconomistGMAT » Mon Jan 24, 2011 12:23 am
It's a smart-alec question: for stat. (2), if 1 is in S, then 1/1=1 must also be in S. I don't think the question demands these to be two different terms (i.e. that set S will then include 1 AND another 1), but it's left ambiguous, which seems slightly off.

Bottom line, it's down to interpretation of the set: if we are to understand that the set includes at least two terms, 1 and 1/1=1, then stat. (2) is sufficient: if we have 1 and 1, we also have 1+1=2, and if we have 1 and 2, we also have 1+2=3., and the answer is "yes".

But if the mere presence of the single term "1" satisfies the terms of the set from the question stem, since both 1 and 1/1 are equal to 1, then we simply do not know whether or not 3 is also in the set - the statement didn't specify that 1 is the ONLY term in the set, which could also include 3, or 3,000, or -10,000,000 as far as we know.
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