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Interest rate. Upstate Bank is offering long-term certificates of deposit with a face value of \( \$ 100,000 \) (future value). Bank customers can buy these CDs today for \( \$ 45,000 \) and will receive the \( \$ 100,000 \) in 20 years. What interest rate is the bank paying on these CDs? What interest rate is the bank paying on these CDs? \( \square \% \) (Round to two decimal plices.)

Ask by Craig Simpson. in the United States
Jan 22,2025

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Tutor-Verified Answer

Answer

The bank is paying an interest rate of approximately 4.07% on these CDs.

Solution

To find the interest rate that the bank is paying on these CDs, we can use the formula for compound interest: \[ A = P(1 + \frac{r}{100})^n \] where: - \( A \) is the future value of the investment (in this case, $100,000), - \( P \) is the present value of the investment (in this case, $45,000), - \( r \) is the interest rate (which we need to find), - \( n \) is the number of years (in this case, 20 years). Given that the present value of the investment is $45,000 and the future value is $100,000, we can rearrange the formula to solve for the interest rate \( r \): \[ 100,000 = 45,000(1 + \frac{r}{100})^{20} \] Now, we can solve for \( r \) to find the interest rate that the bank is paying on these CDs. Solve the equation by following steps: - step0: Solve for \(r\): \(100000=45000\left(1+\frac{r}{100}\right)^{20}\) - step1: Swap the sides: \(45000\left(1+\frac{r}{100}\right)^{20}=100000\) - step2: Divide both sides: \(\frac{45000\left(1+\frac{r}{100}\right)^{20}}{45000}=\frac{100000}{45000}\) - step3: Divide the numbers: \(\left(1+\frac{r}{100}\right)^{20}=\frac{20}{9}\) - step4: Simplify the expression: \(1+\frac{r}{100}=\pm \sqrt[20]{\frac{20}{9}}\) - step5: Simplify: \(1+\frac{r}{100}=\pm \frac{\sqrt[20]{20\times 19683^{2}}}{3}\) - step6: Separate into possible cases: \(\begin{align}&1+\frac{r}{100}=\frac{\sqrt[20]{20\times 19683^{2}}}{3}\\&1+\frac{r}{100}=-\frac{\sqrt[20]{20\times 19683^{2}}}{3}\end{align}\) - step7: Calculate: \(\begin{align}&r=\frac{100\sqrt[20]{20\times 19683^{2}}-300}{3}\\&r=-\frac{100\sqrt[20]{20\times 19683^{2}}+300}{3}\end{align}\) - step8: Rewrite: \(r_{1}=-\frac{100\sqrt[20]{20\times 19683^{2}}+300}{3},r_{2}=\frac{100\sqrt[20]{20\times 19683^{2}}-300}{3}\) The interest rate that the bank is paying on these CDs is approximately 4.07%.

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Extra Insights

To find the interest rate being paid on the CDs, we can use the formula for the future value of a single sum, which is given by: \[ FV = PV(1 + r)^n \] Where: - \( FV \) is the future value, - \( PV \) is the present value, - \( r \) is the interest rate (as a decimal), - \( n \) is the number of years. In this scenario, we have: - \( FV = 100,000 \) - \( PV = 45,000 \) - \( n = 20 \) Rearranging the formula to solve for \( r \): \[ 100,000 = 45,000(1 + r)^{20} \] First, divide both sides by \( 45,000 \): \[ \frac{100,000}{45,000} = (1 + r)^{20} \] This simplifies to: \[ \frac{100}{45} = (1 + r)^{20} \] Next, calculate \( \frac{100}{45} \): \[ 2.2222 \approx (1 + r)^{20} \] Now, take the 20th root of both sides to isolate \( (1 + r) \): \[ 1 + r = (2.2222)^{\frac{1}{20}} \] Calculating this gives: \[ 1 + r \approx 1.08315 \] Subtracting 1: \[ r \approx 0.08315 \] Converting to a percentage gives \( r \approx 8.32\% \). So, the bank is paying an interest rate of approximately \( 8.32\% \).

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