Let a = first term, T1
Let b = Tn+1 - Tn = term difference
a + 9b = 34
S20 = T1 + T2 + ...T19 + T20
= a + (a+b) + (a+2b) + ...(1+19b)
20a + (b)(1+2+3+...19)
= 20 a + 190 b = 710
20a + 180b = 680
10 b = 30
b = 3
a = 34 -27 = 7
Arithmetic Series is
7, 10, 13, 16, 19, 22, 25, 28, 31, 34,...
10th term = 34
Check the sum of the first 20 terms and predict the 25th
the 10th term is 34 of arithmetic series and the sum of the 20th term is 710 i.e S20=710.what is the 25th term?
2 answers
I dont understand the question