Calculating and comparing simple and compound interest

Stacy is comparing two savings accounts. She will deposit $350 in an account, and make no deposits or withdrawals for 5 years. Both accounts have an annual Interest rate of 6%. Account A earns simple interest, and Account B is compounded annually, Which account earns more after 5 years? How much more?

1 answer

To compare the amounts earned in both accounts, we can calculate the total amount for Account A (simple interest) and Account B (compound interest) separately after 5 years.

Account A: Simple Interest

The formula for calculating simple interest is:

\[ A = P + (P \times r \times t) \]

Where:

  • \(A\) is the total amount (principal + interest)
  • \(P\) is the principal amount (initial deposit)
  • \(r\) is the annual interest rate (in decimal)
  • \(t\) is the time (in years)

For Account A:

  • \(P = 350\)
  • \(r = 0.06\)
  • \(t = 5\)

Substituting the values into the formula:

\[ A = 350 + (350 \times 0.06 \times 5) \]

Calculating the interest:

\[ A = 350 + (350 \times 0.3) = 350 + 105 = 455 \]

So, the total amount in Account A after 5 years is $455.

Account B: Compound Interest

The formula for calculating compound interest is:

\[ A = P \times (1 + r)^t \]

Where:

  • \(A\) is the total amount (principal + interest)
  • \(P\) is the principal amount (initial deposit)
  • \(r\) is the annual interest rate (in decimal)
  • \(t\) is the time (in years)

For Account B:

  • \(P = 350\)
  • \(r = 0.06\)
  • \(t = 5\)

Substituting the values into the formula:

\[ A = 350 \times (1 + 0.06)^5 \]

Calculating:

\[ A = 350 \times (1.06)^5 \] \[ A = 350 \times 1.338225 \] \[ A \approx 467.38 \]

So, the total amount in Account B after 5 years is approximately $467.38.

Comparing the two accounts

Now, let's find out how much more Account B earns compared to Account A:

\[ \text{Difference} = A_B - A_A = 467.38 - 455 = 12.38 \]

Conclusion

Account B (compound interest) earns approximately $467.38, while Account A (simple interest) earns $455. Therefore, Account B earns $12.38 more than Account A after 5 years.