Riordan saved $5 in the first week and increased his savings by $7 each week. How much would he have saved at the end of 9 weeks?
Make a list: 5, 12, 19, 26, 33, 40, 47, 54, 61
Using rainbow method: 5 + 61 = 6612 + 54 = 6619 + 47 = 6626 + 40 = 66Sum of each pair = 66Number of pairs: 4, left: 33 Sum of all pairs = [66 x 4] + 33 = 264 + 33 = $297 Answer(s): $297