Debt Payment Plans
1. **State the problem:**
You owe R 500 000 and want to find which of the three payment plans pay closest to this amount without overpaying, considering different interest rates and compounding periods.
2. **Analyze Payment Plan 1:**
- Immediate payment: R 100 000 (no interest)
- Payment at end of 3 years: R 400 000
- Interest rate: 10% compounded annually (assumed)
Calculate the present value (PV) of R 400 000 at 10% for 3 years:
$$PV = \frac{400000}{(1+0.10)^3} = \frac{400000}{1.331} \approx 300526.32$$
Total PV for Plan 1 = 100000 + 300526.32 = 400526.32
3. **Analyze Payment Plan 2:**
- Monthly payment: R 20 000
- Number of months: 3 years × 12 = 36
- Interest rate: 11% pa compounded monthly, so monthly interest rate:
$$i = \frac{0.11}{12} = 0.0091667$$
Calculate the present value of the annuity (payments at the end of each month):
$$PV = P \times \frac{1-(1+i)^{-n}}{i}$$
$$PV = 20000 \times \frac{1-(1+0.0091667)^{-36}}{0.0091667}$$
Calculate:
$$ (1+0.0091667)^{-36} = \frac{1}{(1.0091667)^{36}} \approx \frac{1}{1.432364} = 0.69855$$
$$PV = 20000 \times \frac{1-0.69855}{0.0091667} = 20000 \times \frac{0.30145}{0.0091667} \approx 20000 \times 32.88 = 657592.6$$
4. **Analyze Payment Plan 3:**
- Single payment R 900 000 at end of 3 years
- Interest rate: 11% compounded monthly (monthly rate 0.0091667)
Calculate the present value:
$$PV = \frac{900000}{(1+0.0091667)^{36}} = \frac{900000}{1.432364} \approx 628384.8$$
5. **Compare present values with debt:**
- Plan 1 PV: R 400,526.32 (less than R 500,000)
- Plan 2 PV: R 657,592.6 (more than R 500,000)
- Plan 3 PV: R 628,384.8 (more than R 500,000)
We want to pay closest to R 500,000 without paying more, so Plan 1 is closest but underpays.
6. **Adjust Plan 1 to exactly match R 500,000 debt:**
Present value of first payment today is exact, so let the second payment amount be \(X\):
$$100000 + \frac{X}{(1+0.10)^3} = 500000$$
$$\frac{X}{1.331} = 400000$$
$$X = 400000 \times 1.331 = 532400$$
So, to meet the debt exactly, you must pay R 100,000 today and R 532,400 after 3 years.
**Final answer:**
- Plan closest without overpaying: Plan 1 (present value ~R 400,526.32)
- Amount to pay to meet debt exactly under Plan 1: R 100,000 today and R 532,400 at end of 3 years.