A factory produces 1200 light bulbs in the first hour of a particular day. In each following hour the output falls by 20 light bulbs and the factory runs non-stop for 25 hours.
(i) Explain why the hourly outputs form an arithmetic progression and write its common difference.
(ii) How many light bulbs are produced in the 25th hour?
(iii) Calculate the total number of light bulbs produced during the 25-hour run.