For an arithmetic progression the first term is 120 and the common difference is –4

MATHEMATICS · Multi-part · A Level · Mathematics · Sequences and series · Sequences and series

Problem

For an arithmetic progression the first term is 120 and the common difference is –4. Solve the following: (i) Find the smallest positive integer

n

for which the sum of the first

n

terms is less than or equal to zero. (ii) Compute the sum of the first

(n-1)

terms—the last positive cumulative total just before the result in part (i) occurs.