Asked by Sania

The fourth term of an AP is 10 and eleventh term of it exceeds three times the fourth term by 1. Find the sum of first 20 terms.
Answered by Steve
find a and d using what they have told you:

a+3d = 10
a+10d = 3(a+3d)+1

Then just evaluate

S20 = 20/2 (2a+19d)