Andrew earns an allowance of $12 the first week, $17 the next week, $22 the following week, and so on. How much will Andrew earn over the course of 10 weeks?
Sum them up as an arithmetic series:
N =[L - F] / D + 1
10 =[L - 12] / 5 + 1
L = 57 - last allowance
[F + L] / 2 x N =Sum
Sum =[12 + 57] / 2 x 10
Sum =[69] / 2 x 10
Sum = 34.5 x 10
Sum = $345.00 - Andrew's total allowance over 10-week period.
+15 
