SOLUTION: Mike started a savings account by depositing $9. Each month he deposits more money than the month before. At the end of 41 months, he has saved $9,989.00. How much more does he dep

Question 849684: Mike started a savings account by depositing $9. Each month he deposits more money than the month before. At the end of 41 months, he has saved $9,989.00. How much more does he deposit each month?
Answer by swincher4391(1107) (Show Source): You can put this solution on YOUR website!
sum of arithmetic series:
Sn = (a1 + an) * n / 2
= (9+an)*41/2 = 9989
solving for An we get
An = 478.27
An = A1 + (n-1)*d where d is the common difference
478.27 = 9 + (41-1)*d
478.27 - 9 = 40d
469.27 = 40d
d =

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