Ken wants to get more exercise so he begins by walking for 20 minutes. Each day for two weeks, he increases the length of time that he walks by 5 minutes. At the end of two weeks, the length of time that he has walked each day is given by the following arithmetic sequence: 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 The total length of time that Ken has walked in two weeks is the sum of the terms of this arithmetic sequence: 20+25+30 +35 +40 +45 + 50 +55 +60 +65 +70+ 75 +80+ 85 This sum is called a series.