Question
We describe a savings account with continuous withdrawals that earns interest compounded continuously. Let
denote the money in the account,
years after it was open. Find the differer
equation and initial condition that
satisfies.
Initial amount
, annual interest rate
, withdrawals at the rate of
per month
equation and initial condition that
Initial amount
Ask by Evans Simmons. in the United States
Mar 23,2025
Upstudy AI Solution
Tutor-Verified Answer
Answer
The differential equation for the account balance
is:
with the initial condition:
Solution
We are given an account with an initial amount of
, earning interest at an annual rate of
(compounded continuously), and with continuous withdrawals at the rate of
per month. Since withdrawals are monthly, we convert this rate to an annual rate:
Let
denote the balance in the account as a function of time
(in years). The changes in
are due to the interest earned and the withdrawals made. The differential equation is set up as follows:
- The interest contributes a rate of change given by
(because the interest is 2% per year). - The withdrawals contribute a negative rate of change of
per year.
Thus, the differential equation that
satisfies is
The initial condition is given by the initial deposit:
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Extra Insights
To model this situation, we start with the differential equation for continuous compounding with continuous withdrawals. The money in the account grows at an interest rate
while simultaneously decreasing due to the withdrawals.
The equation will be of the form:
where
is the total rate of withdrawals per year. The monthly withdrawal amount is $500, so the annual withdrawal rate is
. Therefore, the equation becomes:
The initial condition is defined as the amount in the account when it was opened: