A call centre handles (35) calls in the first hour and (5) more calls each next hour. How many calls are handled in the (8)th hour?

Correct answer: 70

The number of calls forms an arithmetic progression (AP) with first term 35 and common difference 5. The calls handled in the 8th hour are \(a_8=35+(8-1)\times5=35+35=70\). Therefore, 70 is correct. The value 65 results from counting only 6 increases, but there are 7 increases from the first hour to the eighth hour. Exam tip: use \(a_n=a+(n-1)d\) for the nth term of an AP.