In an arithmetic progression the sum of the first 12 terms is 450 and the 13th term is 70.
MATHEMATICS · Multi-part · A Level · Mathematics · Sequences and series · Sequences and series
Problem
In an arithmetic progression the sum of the first 12 terms is 450 and the 13th term is 70.
(i) If the first term is a and the common difference is d, write two equations that arise from the information given.
(ii) Determine the values of a and d.
(iii) Using the values found, find the sum of the first 25 terms of the progression.