Question

if the interest rate on a savings account is 0.018%, approximately how much money do you need to keep in this account for 1 year to earn enough interest to cover a single $9.99 Below-Minimum-Balance Fee?

Answer 1

A = $9.99, the amount needed after 1 year
r = 0.018% = 0.00018, interest rate
n = 12, compoundings per year
t = 1, one year duration

Let P = required balance at the beginning of the year.
Then

`P(1+ (r)/(n) )^(nt) = A`
P(1 + 0.00018/12)¹² = 9.99
1.00018P = 9.99
P = $9.988 ≈ $9.99

Answer: $9.99