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In a certain series, each term except...

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In a certain series, each term except...

by BTGmoderatorLU » Thu Oct 26, 2017 5:45 am
In a certain series, each term except for the two first terms is the sum of the two previous terms. What is the value of the first term in the series?

(1) The third term is 2.
(2) The fourth term is 3.

The OA is C.

I don't have it clear. Can any expert help me with this DS question please? Thanks.
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Source: — Data Sufficiency |

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by Jay@ManhattanReview » Thu Oct 26, 2017 6:38 am
LUANDATO wrote:In a certain series, each term except for the two first terms is the sum of the two previous terms. What is the value of the first term in the series?

(1) The third term is 2.
(2) The fourth term is 3.

The OA is C.

I don't have it clear. Can any expert help me with this DS question please? Thanks.
(1) The third term is 2:

Say the first two terms are a and b, respectively.

Thus, we have a + b = 2.

Thus, the first three terms are: a, b, and 2.

We cannot get the value of a. Insufficient.

(2) The fourth term is 3:

We cannot We cannot get the value of a. Insufficient.

(1) and (2) combined:

From (1), we have a + b = 2 and from (2), we have b + 2 = 3 => b = 1 and a = 1. Sufficient.

The correct answer: C

Hope this helps!

-Jay

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