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S is a sequence such that Sn = (-1)^n for each integer n ≥ 1. What is

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Joined: 02 Sep 2009
Posts: 58445
S is a sequence such that Sn = (-1)^n for each integer n ≥ 1. What is  [#permalink]

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17 Dec 2018, 02:01
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5% (low)

Question Stats:

86% (00:48) correct 14% (00:29) wrong based on 40 sessions

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S is a sequence such that $$S_n = (-1)^n$$ for each integer n ≥ 1. What is the sum of the first 20 terms in S?

A. -1
B. 0
C. 1
D. 10
E. 20

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Re: S is a sequence such that Sn = (-1)^n for each integer n ≥ 1. What is  [#permalink]

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17 Dec 2018, 03:44
Bunuel wrote:
S is a sequence such that $$S_n = (-1)^n$$ for each integer n ≥ 1. What is the sum of the first 20 terms in S?

A. -1
B. 0
C. 1
D. 10
E. 20

s1,s3,s5... s19= -1
s2,s4,s6..s20=1

total odd& even terms are both 10 each for 10*(-1)+10(1)= 0 IMO B
Re: S is a sequence such that Sn = (-1)^n for each integer n ≥ 1. What is   [#permalink] 17 Dec 2018, 03:44
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