Independent solution

How to solve this Perpetuity Duration Sensitivity question

Setup

Setup

The stream begins immediately, so price it as a perpetuity-due at 7%.

L=10,0001.070.07=152,857.14L=10{,}000\frac{1.07}{0.07}=152{,}857.14

Model

Model

Use the modified duration of a level perpetuity-due.

Dmod=10.07(1.07)=13.351135D_{\mathrm{mod}}=\frac{1}{0.07(1.07)}=13.351135

Compute

Compute

Apply the yield change from 7% to 5% in the first-order price formula.

Δi=0.02\Delta i=-0.02
M=L(1DmodΔi)=193,673.47M=L(1-D_{\mathrm{mod}}\Delta i)=193{,}673.47
ML=40,816.33M-L=40{,}816.33

Answer

Answer

The estimated increase is 40816, choice A.

ML40,816(A)\boxed{M-L\approx40{,}816\quad\text{(A)}}