Independent solution

How to solve this Growing Perpetuity Duration question

Setup

Setup

Discounted payments in the growing perpetuity form a geometric sequence with ratio q = 1.02/1.05. Treat q as the discount factor for an equivalent level perpetuity.

q=1.021.05=11+jq=\frac{1.02}{1.05}=\frac1{1+j}

Model

Model

The weighted-average payment time is therefore the level-perpetuity duration under the net rate, equal to (1 + i)/(i − g).

DM=1dj=1+jjD_M=\frac1{d_j}=\frac{1+j}{j}

Compute

Compute

Using i = 5% and g = 2% gives 1.05/0.03 = 35 years.

DM=1.050.050.02=35D_M=\frac{1.05}{0.05-0.02}=35

Answer

Answer

The calculation gives 35 for growing perpetuity duration, matching published choice B.

DM=35(B)\boxed{D_M=35\quad\text{(B)}}