gmatbusters wrote:
Project DS Butler: Day 1: Data Sufficiency (DS1)
For DS butler Questions Click HereWhat is the 1st term in sequence S ?
(1) The 3rd term in S is 2.
(2) The 2nd term in S is twice the 1st, and the 3rd term is three times the 2nd.
Target question: What is the 1st term in sequence S ? Statement 1: The 3rd term in S is 2 Since we're not given any information about the NATURE of the sequence, there's no way to answer the
target question with certainty.
So, statement 1 is NOT SUFFICIENT
Statement 2: The 2nd term in S is twice the 1st, and the 3rd term is three times the 2nd.Great, we're given information about the NATURE of the sequence, but we aren't given the VALUE of any terms.
For example, consider these two possible cases that satisfy statement 2:
Case a: The first 3 terms are: {1, 2, 6....}. In this case, the answer to the target question is
the 1st term is 1 Case b: The first 3 terms are: {3, 6, 18....}. In this case, the answer to the target question is
the 1st term is 3 Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined Statement 1 tells us that the 3rd term in S is
2Statement 2 tells us that
the 3rd term is three times the 2nd. So, if the 3rd term is
2, then the 2nd term must be
2/3Statement 2 also tells us that
the 2nd term in S is twice the 1st. So, if the 2nd term is
2/3, then
the 1st term must be 1/3Since we can answer the
target question with certainty, the combined statements are SUFFICIENT
Answer: C
Cheers,
Brent
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Brent Hanneson – Creator of gmatprepnow.com
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