Compound Interest 86Baf0
1. **Problem statement:** We want to find the present deposit amount $P$ that will grow to $20,000$ in $9$ years with an annual interest rate of $5\%$ compounded monthly.
2. **Formula used:** The compound interest formula is
$$ A = P \left(1 + \frac{r}{n}\right)^{nt} $$
where:
- $A$ is the amount after time $t$
- $P$ is the principal (initial deposit)
- $r$ is the annual interest rate (decimal)
- $n$ is the number of compounding periods per year
- $t$ is the time in years
3. **Given values:**
- $A = 20000$
- $r = 0.05$
- $n = 12$ (monthly compounding)
- $t = 9$
4. **Rearranging the formula to solve for $P$:**
$$ P = \frac{A}{\left(1 + \frac{r}{n}\right)^{nt}} $$
5. **Calculate the denominator:**
$$ 1 + \frac{0.05}{12} = 1 + 0.0041667 = 1.0041667 $$
$$ nt = 12 \times 9 = 108 $$
$$ \left(1.0041667\right)^{108} \approx 1.551328 $$
6. **Calculate $P$:**
$$ P = \frac{20000}{1.551328} \approx 12889.46 $$
7. **Answer:** You need to deposit approximately **12889.46** today to have 20000 after 9 years at 5% annual interest compounded monthly.