An AP is given k,2k/3,k/3,0....calculate the sum of the first 30 terms

Answer 1

clearly d = -k/3

S30 = 30/2 (2k + 29(-k/2)) = -375k/2

Answer 2

small typo in Steve's answer:

last line should be

S30 = 30/2 (2k + 29(-k/3))
= 15(-23k/3)
= -115k