Independent solution

How to solve this Unit-Payment Loan Amortization Identities question

Setup

Setup

The time-zero principal of a unit-payment n-period loan is the annuity-immediate value.

L=aniL=a_{\overline n|i}

Model

Model

The borrower makes n payments of one, so the undiscounted total paid is n.

total payments=n\text{total payments}=n

Compute

Compute

Total paid decomposes into principal repaid plus interest paid.

total interest=nL=nani\text{total interest}=n-L=n-a_{\overline n|i}

Answer

Answer

This identity is precisely choice A.

total interest=nani(A)\boxed{\text{total interest}=n-a_{\overline n|i}\quad\text{(A)}}