2026 IGCSE Additional Mathematics May/June 0606/12 Q4

An arithmetic progression has first term \(u_1=400\) and common difference \(d=-2\).

1. Find the 81st term and the 100th term.[2]
2. Find the sum of all the terms from the 81st to the 100th, \(u_{81}+u_{82}+\ldots+u_{100}\).[3]