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Find S_25 for -7+-2+3+8+.

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elieli7 | eNotes Newbie

Posted July 18, 2013 at 2:06 AM via web

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Find S_25 for -7+-2+3+8+.

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llltkl | College Teacher | Valedictorian

Posted July 18, 2013 at 2:15 AM (Answer #1)

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The series is in A.P. with first term, a= -7 and common difference, d= 5.

Sum of an A.P. upto the nth term is given by:

`S_n=n/2(2a+(n-1)d)`

Plugging in the values, sum upto the 25th term is given by

`S_(25)=25/2(2*(-7)+(25-1)5)`

`=25/2((-14)+120)`

`=25/2(106)`

`=1325`

=>answer.

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