Loan Balance
1. **Problem Statement:** Cindy borrows money and repays with monthly payments of 889 at the beginning of every month. Interest rate is 9.902% per year, compounded monthly, and loan is paid off after 4 payments. We want to find how much she owes immediately before payment 3.
2. **Given Data:**
- Monthly payment, $P = 889$
- Annual nominal interest rate, $i_{annual} = 9.902\% = 0.09902$
- Number of payments, $n = 4$
- Payments are made at the beginning of the month (annuity due)
3. **Calculate monthly interest rate:**
$$ i = \frac{0.09902}{12} = 0.0082517 $$
4. **Relevant formula:**
Loan amount $L$ satisfies the present value of an annuity due:
$$ L = P \times \frac{1 - (1+i)^{-n}}{i} \times (1+i) $$
5. **Calculate loan amount:**
$$ L = 889 \times \frac{1-(1.0082517)^{-4}}{0.0082517} \times 1.0082517 $$
Calculate each part:
$$ (1.0082517)^{-4} = \frac{1}{(1.0082517)^4} = \frac{1}{1.0334} = 0.9677 $$
$$ 1 - 0.9677 = 0.0323 $$
$$ \frac{0.0323}{0.0082517} = 3.9151 $$
$$ L = 889 \times 3.9151 \times 1.0082517 = 889 \times 3.9476 = 3508.02 $$
Loan amount is approximately $3508.02$.
6. **Find amount owed immediately before payment 3:**
After payments 1 and 2, the principal will reduce, but we want the balance just before payment 3, so after interest accrual on the previous balance, but before payment 3 is made.
7. **Step 1: Calculate balance immediately after payment 2 (start of month 3):**
Using annuity due, the balance after $k$ payments at beginning of periods is:
$$ B_k = L \times (1+i)^k - P \times \frac{(1+i)^k - 1}{i} $$
For $k=2$:
$$ B_2 = 3508.02 \times (1.0082517)^2 - 889 \times \frac{(1.0082517)^2 -1}{0.0082517} $$
Calculate powers:
$$ (1.0082517)^2 = 1.01658 $$
Calculate numerator for payment term:
$$ 1.01658 -1 = 0.01658 $$
Payment factor:
$$ \frac{0.01658}{0.0082517} = 2.0094 $$
Calculate:
$$ 3508.02 \times 1.01658 = 3566.17 $$
$$ 889 \times 2.0094 = 1786.36 $$
Balance before payment 3:
$$ B_2 = 3566.17 - 1786.36 = 1779.81 $$
8. **Interpretation:** Immediately before payment 3, Cindy owes about 1779.81.
**Final Answer: $1779.81$