zisis wrote:
Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is negative
(2) The fourth term in S is positive
The book claims this is one of the most diff questions GMAT can produce which I believe it is a joke....nevertheless got it wrong because I mis-interpreted the question. I am posting to see if more people will mis-interpret or if it is just me that is going *o*kers
Answer cannot be B, it should be A.
Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?
(1) The third term in S is negative --> first and second terms must have opposite signs so we can hve following two scenarios:
-+--+--+--+-...
OR:
+--+--+--+--...
You can see that in both cases there is a repeated pattern of three terms in which 2 are negative and 1 positive (-+- or +--) so in both cases out of 24 terms 2/3 will be negative, so there will be 16 negative terms. Sufficient.
(2) The fourth term in S is positive --> either all terms are positive, so zero negatives or +--+... and not all terms are positive, so more than zero negatives. Not sufficient.
Answer: A.
If the OA is B then it should be:Sequence S consists of 24 nonzero integers. If each term in S after the second is the product of the previous two terms, how many terms in S are negative?(1) The third term in S is
positive --> either all terms are positive, so zero negatives or
+--... and not all terms are positive, so more than zero negatives. Not sufficient.
(2) The fourth term in S is
negative --> again two cases:
--+--+--+...OR
-+--+--+-...The same here: in both cases there is a repeated pattern of three terms in which 2 are negative and 1 positive (--+ or -+-) so in both cases out of 24 terms 2/3 will be negative, so there will be 16 negative terms. Sufficient.
Answer: B.
Hope it's clear.