A man plans to buy a $150 000 house. He wants to make a down payment of $30 000 and to take out a 30-year mortgage for the remaining $120 000, at 10% per year, compounded monthly. How much must he repay each month?
Equation (2.6), with the appropriate substitutions, gives
A/P = \frac{i(1 + i)^n}{(1 + i)^n – 1} = \frac{i}{1 – (1 + i)^{-n}} (2.6) \\\\ A = \$120 000\frac{(0.10/12)(1 + 0.10/12)^{(12)(30)}}{(1 – 0.10/12)^{(12)(30)} – 1} = \$120 000\frac{0.16531}{18.8374} = \$1053.08The solution can also be approximated by use of (3.6):
\underset{n→∞}{\lim}(A/P, i\%, n) = i (3.6)A = $120 000(A/P, 10%, 360) ≈ $120 000(0.10/12) = $1000