Ahmad saved $4 in the first week and increased his savings by $4 each week. How much would he have saved at the end of 9 weeks?
Make a list: 4, 8, 12, 16, 20, 24, 28, 32, 36
Using rainbow method: 4 + 36 = 408 + 32 = 4012 + 28 = 4016 + 24 = 40Sum of each pair = 40Number of pairs: 4, left: 20 Sum of all pairs = [40 x 4] + 20 = 160 + 20 = $180 Answer(s): $180