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Sequence

by BTGmoderatorRO » Mon Sep 18, 2017 1:44 pm
If the sequence S has 300 terms, what is the 293rd term of S?
(1) The 298th term of S is -616, and each term of S after the first is 2 less than the preceding term.
(2) The first term of S is -22.

a. statement 1 and 2 are insufficient
b. statement 1 is sufficient and statement 2 is insufficient
c. statement 1 is insufficient and statement 2 is sufficient
d. Both statement are sufficient
OA is b

what is wrong with statement 1 and 2 in this question?
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Source: — Data Sufficiency |

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by Brent@GMATPrepNow » Mon Sep 18, 2017 2:12 pm
I am reposting the question with the ORIGINAL/OFFICIAL 5 answer choices that accompany all GMAT Data Sufficiency questions.
If the sequence S has 300 terms, what is the 293rd term of S?

(1) The 298th term of S is -616, and each term of S after the first is 2 less than the preceding term.
(2) The first term of S is -22.

(A) Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
(B) Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
(C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
(D) EACH statement ALONE is sufficient.
(E) Statements (1) and (2) TOGETHER are NOT sufficient.

Answer: A
Target question: What is the 293rd term of S?

Statement 1: The 298th term of S is -616, and each term of S after the first is 2 less than the preceding term.
So, each term is 2 less than the previous term.
Since term_298 = -616, we can conclude that:
term_297 = -614
term_296 = -612
term_295 = -610
So, we COULD keep going to determine the value of term_293 (which happens to be -606)
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: The first term of S is -22.
Since this statement tells us nothing about the NATURE of the sequence, there's no way to determine the value of term_293
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Answer: A

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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