Math Problem Statement

You deposit $300 each month into an account earning 8% interest compounded monthly.

a) How much will you have in the account in 25 years?

Solution

To solve this problem, we can use the formula for the future value of a series of monthly deposits with compound interest:

A=P((1+r)n1r)A = P \left( \frac{(1 + r)^n - 1}{r} \right)

Where:

  • AA is the future value of the account after the deposits and interest,
  • PP is the monthly deposit amount ($300),
  • rr is the monthly interest rate (annual rate divided by 12),
  • nn is the total number of deposits (number of months),
  • tt is the number of years.

Step 1: Identify the variables

  • P=300P = 300 (monthly deposit),
  • Annual interest rate = 8%, so monthly interest rate r=8%12=0.0812=0.00667r = \frac{8\%}{12} = \frac{0.08}{12} = 0.00667,
  • n=25×12=300n = 25 \times 12 = 300 months (for 25 years).

Step 2: Apply the formula

A=300×((1+0.00667)30010.00667)A = 300 \times \left( \frac{(1 + 0.00667)^{300} - 1}{0.00667} \right)

Now, we can calculate the result:

  1. (1+0.00667)300=(1.00667)3006.84848(1 + 0.00667)^{300} = (1.00667)^{300} \approx 6.84848
  2. Subtract 1: 6.848481=5.848486.84848 - 1 = 5.84848
  3. Divide by the interest rate: 5.848480.00667876.78\frac{5.84848}{0.00667} \approx 876.78
  4. Multiply by the monthly deposit: 300×876.78263,034300 \times 876.78 \approx 263,034

Final Answer:

You will have approximately $263,034 in the account after 25 years.

Would you like more details on any step or have further questions?

Here are some related questions:

  1. How would the total change if you deposit for 30 years instead?
  2. What if the interest rate was 6% instead of 8%?
  3. How much of the total amount comes from the interest earned?
  4. What would the final amount be with quarterly compounding?
  5. How would a one-time lump sum deposit compare to monthly deposits over time?

Tip: Increasing the deposit frequency (e.g., biweekly instead of monthly) can slightly increase the final balance due to more frequent compounding.

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Math Problem Analysis

Mathematical Concepts

Compound Interest
Series of Deposits
Exponential Growth

Formulas

A = P * ((1 + r)^n - 1) / r

Theorems

Compound Interest Theorem

Suitable Grade Level

Grades 10-12