Asked by Fernando

An arithmetic series is such that the 10th term is 40 and the sum of the first 10 terms is 265. Find the sum of the first 20 terms.

Answers

Answered by Steve
T10 = a+9d = 40
S10 = 10/2 (a+40) = 265
a = 13
so, d=3

S20 = 20/2 (2*13+19*3) = 830
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