SOLUTION: How many terms of the arithmetic sequence -3, 2, 7,... must be added together for the sum of the series to be 116?

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Question 1022272: How many terms of the arithmetic sequence -3, 2, 7,... must be added together for the sum of the series to be 116?
Answer by satyareddy22(84) About Me  (Show Source):
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The sum of arithmetic sequence = (n/2)[2a+(n-1)d]=116
where n=number of terms in the series
a=first number in series= -3
d=common difference= 5
(n/2)[2(-3)+(n-1)5]=116
(n)[-6+5n-5]=116*2
(n)[5n-11]=232
5n^2-11n-232=0
solving equation , we get
n=8