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Adriana Ayers

Adriana Ayers

Answered question

2022-06-21

My initial investment is $ 100, and I earn 1 % interest per day. I can opt for any number of compoundings per day (if twice per day, then the interest rate per compounding period is 0.5 % , and so on), but I have to pay $ 0.01 each time my interest is compounded. After 365 days I will close the account.
What would this equation look like, and how should I include this to maximize my total deposit? How to generalize and figure out a good or optimal maximization?

Answer & Explanation

Marlee Guerra

Marlee Guerra

Beginner2022-06-22Added 25 answers

Let m be the number of compound periods per day.

Then T n + 1 = T n ( 1 + 0.01 m ) 0.01 ( n 0 ) .

This is a first-order linear recurrence relation; derive the closed-form expression for T n .

The task is to finally determine the positive integer m at which T 365 m is greatest (among the positive integer values of m).

(Alternatively, the answer is easy to determine by simply varying m in the above equation and observing the effect.)

Additionally, the closed-form formula above for T n also reveals that

1. m = 100 you will collect exactly $ 100 when closing the account;
2. 100 < m < 103 you will collect less than your $ 100 principal when closing the account;
3. m 103 you will be owing money when closing the account.

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