Independent solution

How to solve this Loan Balances and Amortization question

Setup

Setup

With t denoting the payment number, the principal portion is the payment discounted for the remaining-payment count.

Pt=Rv21tP_t=Rv^{21-t}
It=RPtI_t=R-P_t

Model

Model

Set principal and interest equal, which makes each one-half of the level payment.

Rv21t=R/2Rv^{21-t}=R/2
v21t=0.5v^{21-t}=0.5

Compute

Compute

At 5%, solving gives t = 6.793301, so the nearest installment is 7.

t=21ln2ln1.05=6.79330092t=21-\frac{\ln2}{\ln1.05}=6.79330092

Answer

Answer

The portions are most nearly equal in the 7th installment, selecting choice B.

t7(B)\boxed{t\approx7\quad\text{(B)}}