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1000 DS

by radhika1306 » Wed Aug 29, 2007 5:38 am
S is a set of integers such that
i) if a is in S, then –a is in S, and
ii) if each of a and b is in S, then ab is in S.
Is –4 in S?
(1) 1 is in S.
(2) 2 is in S.
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by agps » Wed Aug 29, 2007 7:21 am
My guess is B.

-4 would exist if and only if:
4 exists OR ab=4 or -4;

from 1) 1 exists, so -1 exits 1*(-1) = -1 not sufficient
from 2) 2 exists, so -2 exists 2*(-2) = -4, so -4 exists sufficient
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by radhika1306 » Thu Aug 30, 2007 11:56 am
correct thank you
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