A girl saves money over 200 weeks. She saves 5p in Week 1, 7p in Week 2, 9p in Week 3, and so on until Week 200. Her weekly savings form an arithmetic sequence. Find the amount she saves in Week 200. Calculate total savings over the 200 week period.

In part (a) the majority obtained 403 and some wrote their answer as £4.03, there was the usual crop of arithmetic errors with 2 ×199 = 298 or 498 being quite common. In part (b) the sum formula was usually quoted and used correctly but again arithmetic slips (e.g.408 ×100 = 4080 or 10 + 398 = 418 or 498) were often seen and some made errors with the units giving the answer as £40800.