The 9th term of an AP is 52 while the 12 term is 70 find the sum of the 20 terms.

3 answers

answers
https://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html
a+8d = 52
a+11d = 70
Now find a and d, and then
S20 = 20/2 (2a+19d)