Quarterly Deposits
1. **State the problem:**
We want to find the quarterly deposit amount needed so that after 5 years, with interest compounded quarterly at 7.5% per year, the company will have R900000.
2. **Identify variables and formulas:**
- Future value needed, $FV = 900000$
- Annual interest rate, $r = 7.5\% = 0.075$
- Compounded quarterly, so interest rate per quarter, $i = \frac{0.075}{4} = 0.01875$
- Number of quarters in 5 years, $n = 5 \times 4 = 20$
- Deposit amount per quarter = $P$, which is what we want to find.
3. **Use the formula for the future value of an ordinary annuity:**
$$FV = P \times \frac{(1+i)^n - 1}{i}$$
Rearranged to solve for $P$:
$$P = \frac{FV \times i}{(1+i)^n - 1}$$
4. **Calculate denominator:**
$$ (1+i)^n - 1 = (1 + 0.01875)^{20} - 1 = 1.01875^{20} - 1 $$
Calculate $1.01875^{20}$:
$$ 1.01875^{20} \approx 1.45144 $$
So,
$$1.45144 - 1 = 0.45144$$
5. **Calculate $P$:**
$$ P = \frac{900000 \times 0.01875}{0.45144} = \frac{16875}{0.45144} \approx 37368.96 $$
6. **Interpretation:**
The company needs to deposit approximately R37368.96 at the end of every quarter starting in 3 months to haveR900000 in the fund after 5 years.