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In an arithmetic series, the 15th term is 43 and the sum of the first 15 terms is 120. Add the first 20 terms of the series.
1 answer
a+14d = 43
15/2 (2a+14d) = 120
(a,d) = (-27,5)
S20 = 20/2 (2a+19d) = 410
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