Annuity Duration
1. **State the problem:**
Farah has 600000 in her RRSP and wants to buy an annuity that pays 3500 monthly with an interest rate of 5% compounded annually. We need to find how long (in months) she will receive payments.
2. **Identify variables:**
- Present value (PV) = 600000
- Monthly payment (PMT) = 3500
- Annual interest rate (r) = 5% = 0.05
- Monthly interest rate (i) = \frac{0.05}{12} = 0.0041667
- Number of months (n) = ?
3. **Use the present value of an ordinary annuity formula:**
$$PV = PMT \times \frac{1 - (1 + i)^{-n}}{i}$$
4. **Plug in known values:**
$$600000 = 3500 \times \frac{1 - (1 + 0.0041667)^{-n}}{0.0041667}$$
5. **Isolate the term with n:**
$$\frac{600000 \times 0.0041667}{3500} = 1 - (1.0041667)^{-n}$$
Calculate left side:
$$\frac{600000 \times 0.0041667}{3500} = \frac{2500}{3500} = 0.7142857$$
So,
$$0.7142857 = 1 - (1.0041667)^{-n}$$
6. **Solve for the exponential term:**
$$(1.0041667)^{-n} = 1 - 0.7142857 = 0.2857143$$
7. **Take natural logarithm of both sides:**
$$-n \ln(1.0041667) = \ln(0.2857143)$$
8. **Calculate logarithms:**
$$\ln(1.0041667) \approx 0.004158$$
$$\ln(0.2857143) \approx -1.25276$$
9. **Solve for n:**
$$-n \times 0.004158 = -1.25276$$
$$n = \frac{1.25276}{0.004158} \approx 301.3$$
10. **Round to nearest month:**
$$n \approx 301 \text{ months}$$
**Final answer:** Farah will receive payments for approximately **301 months**.