assuming you mean the first 8 terms and the first 20 terms, then
8/2 (2a+7d) = 160
20/2 (2a+19d) = 880
solve for a and d, and then you want
a_43 = a+42d
The sum of 8 terms of an A.p is 160 while the sum of 20 terms is 880 find the 43 term
1 answer