Retirement Annuity
1. **State the problem:**
Ashley buys an annuity paying $2,500 every six months for 11 years, then $100 every month for 4 years. Interest rate is 2.1% compounded quarterly. We want to find:
a) The purchase price (present value) of the annuity.
b) The total interest received.
2. **Formulas and rules:**
The present value (PV) of an annuity is calculated by:
$$PV = P \times \frac{1 - (1 + i)^{-n}}{i}$$
where $P$ is the payment per period, $i$ is the interest rate per period, and $n$ is the number of periods.
Since the interest is compounded quarterly (4 times a year), the quarterly interest rate is:
$$i_q = \frac{2.1}{100} \div 4 = 0.00525$$
We must adjust the interest rate per payment period for each annuity phase.
3. **Calculate present value of first annuity (11 years, payments every 6 months):**
- Number of payments: $11 \times 2 = 22$
- Interest rate per 6 months (2 quarters):
$$i_1 = (1 + i_q)^2 - 1 = (1 + 0.00525)^2 - 1 = 0.0105$$
- Payment per period: $2500$
Calculate PV:
$$PV_1 = 2500 \times \frac{1 - (1 + 0.0105)^{-22}}{0.0105}$$
Calculate $(1 + 0.0105)^{-22}$:
$$= (1.0105)^{-22} = \frac{1}{(1.0105)^{22}} \approx \frac{1}{1.254} = 0.797$$
So:
$$PV_1 = 2500 \times \frac{1 - 0.797}{0.0105} = 2500 \times \frac{0.203}{0.0105} = 2500 \times 19.33 = 48325$$
4. **Calculate present value of second annuity (4 years, payments every month):**
- Number of payments: $4 \times 12 = 48$
- Interest rate per month (quarterly rate converted to monthly):
$$i_2 = (1 + i_q)^{\frac{1}{3}} - 1 = (1.00525)^{\frac{1}{3}} - 1 \approx 0.00175$$
- Payment per period: $100$
Calculate PV at the time the second annuity starts (after 11 years):
$$PV_2 = 100 \times \frac{1 - (1 + 0.00175)^{-48}}{0.00175}$$
Calculate $(1 + 0.00175)^{-48}$:
$$= (1.00175)^{-48} = \frac{1}{(1.00175)^{48}} \approx \frac{1}{1.088} = 0.919$$
So:
$$PV_2 = 100 \times \frac{1 - 0.919}{0.00175} = 100 \times \frac{0.081}{0.00175} = 100 \times 46.29 = 4629$$
5. **Discount $PV_2$ back 11 years to present value:**
- Number of quarters in 11 years: $11 \times 4 = 44$
- Discount factor:
$$DF = (1 + i_q)^{-44} = (1.00525)^{-44} = \frac{1}{(1.00525)^{44}} \approx \frac{1}{1.254^2} = \frac{1}{1.572} = 0.636$$
So present value of second annuity:
$$PV_2^{present} = 4629 \times 0.636 = 2945$$
6. **Total purchase price:**
$$PV = PV_1 + PV_2^{present} = 48325 + 2945 = 51270$$
7. **Calculate total amount received:**
- First annuity total payments:
$$2500 \times 22 = 55000$$
- Second annuity total payments:
$$100 \times 48 = 4800$$
- Total payments:
$$55000 + 4800 = 59800$$
8. **Calculate interest received:**
$$\text{Interest} = \text{Total payments} - \text{Purchase price} = 59800 - 51270 = 8530$$
**Final answers:**
a) Purchase price of the annuity is approximately $51270.00.
b) Interest received from the annuity is approximately $8530.00.