Independent solution

How to solve this Duration and Convexity question

Setup

Setup

For an end-of-year level perpetuity, duration has the closed form one plus the reciprocal of yield.

DM(i)=1+ii=1+1iD_M(i)=\frac{1+i}{i}=1+\frac1i

Model

Model

The original duration therefore determines the reciprocal yield as 16.6.

17.6=1+1ii=116.617.6=1+\frac1i\Longrightarrow i=\frac1{16.6}

Compute

Compute

Doubling the yield halves that reciprocal component but leaves the leading one unchanged.

DM(2i)=1+12i=1+16.62=9.3D_M(2i)=1+\frac1{2i}=1+\frac{16.6}{2}=9.3

Answer

Answer

The new Macaulay duration is 9.3 years, which is choice B.

DM(2i)=9.3(B)\boxed{D_M(2i)=9.3\quad\text{(B)}}