Independent solution

How to solve this Geometric Perpetuities question

Setup

Setup

Let P be the sale price and let r = -0.02 be the annual payment growth rate.

P=Kir=Ki+0.02P=\frac{K}{i-r}=\frac{K}{i+0.02}

Model

Model

The mistaken calculation used an 8.7% yield and first payment 1500, which determines the price the company intended to charge.

P=1,5000.087+0.02P=\frac{1{,}500}{0.087+0.02}

Compute

Compute

Keep that price fixed and replace the mistaken yield with 7.8%.

K=P(0.078+0.02)K=P(0.078+0.02)
K=1,5000.0980.107=1,373.832K=1{,}500\frac{0.098}{0.107}=1{,}373.832

Answer

Answer

The corrected first payment rounds to 1374, choice D.

K1,374(D)\boxed{K\approx1{,}374\quad\text{(D)}}