A loan of \(\$ 1000\) is to be amortized with quarterly installments of \(\$ 100\)
for as long as necessary plus a smaller final payment one quarter after the
last regular payment. Interest is computed at \(12 \%\) convertible quarterly on
the first \(\$ 500\) of outstanding loan balance and at \(8 \%\) convertible
quarterly on any excess.
a) Find the principal repaid in the fourth installment.
b) Show that prior to the "crossover" point, the successive principal
repayments plus a constant form a geometric progression, i.e.
$$\frac{P_{t+1}+k}{P_{t}+k}=1+j \text { for } t=1,2, \ldots, a-1$$
(1) Find k.
(2) Find \(j\)