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Re: In a sequence a1, a2,…, each term after the first is found [#permalink]
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Carcass wrote:

This question is part of GREPrepClub - The Questions Vault Project



In a sequence a1, a2,…, each term after the first is found by taking the negative of the preceding term, and adding 1. If a1 = 2, what is the sum of the first 99 terms?

(A) 49
(B) 50
(C) 51
(D) 99
(E) 101


a1 = 2

a2 = -1

a3 = 2

a4 = -1

a5 = 2

a6 = -1

We see that each odd/even pair sums to positive 1.

There are 49 even/odd pairs in the first 98 terms; hence, the sum is 49. Since a99 is an odd-numbered term, a99 = 2. So the sum of the first 99 terms is 49 + 2 = 51.

Answer: C
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Re: In a sequence a1, a2,…, each term after the first is found [#permalink]
i have a doubt how are there 50 odd terms in the first 99 terms. Please elaborate cause when they mention first 99 terms do they mean inclusive or exclusive and also when they mention first 99 terms is the 100th number also included?
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Re: In a sequence a1, a2,, each term after the first is found [#permalink]
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Re: In a sequence a1, a2,, each term after the first is found [#permalink]
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