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A sequence An is there such that An=An-1-An-2 where n are in

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Source: — Data Sufficiency |

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by Jay@ManhattanReview » Thu May 04, 2017 12:34 am
ziyuenlau wrote:A sequence An is there such that An=An-1-An-2 where n are integers greater than 2. What is the value of A5?

(1) A4-A3=3
(2) A14=1

Source : Math Revolution
OA=D
We have An=An-1-An-2

Statement 1: A4-A3=3

As per the given relationship, A5 = A4 - A3

=> A5 = 3. Sufficient.

Statement 2: A14=1

A14 = A13 - A12 = A12 - A11- A12 = - A11 = -A10 + A9 = -A9+A8+A9 = A8 = A7-A6 = A6-A5-A6 = -A5

=> A5 = -A14 = -1. Sufficient.

Though each statement is sufficient by itself, the answers from each are not the same.

Either A5 = 3 or A5 = -1. It cannot be both. It seems that one of the statement is incorrectly typed.

The correct answer: D

Hope this helps!

Relevant book: Manhattan Review GMAT Number Properties Guide

-Jay
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