Independent solution

How to solve this Duration and Convexity question

Setup

Setup

Place the first block at times zero through 19 and the second, larger block at times 20 through 49.

PV=Xa¨200.02+4Xv20a¨300.02=78.1729XPV=X\ddot a_{\overline{20}|\,0.02}+4Xv^{20}\ddot a_{\overline{30}|\,0.02}=78.1729X

Model

Model

Duration requires both ordinary present value and a time-weighted present value; the payment scale X will cancel.

M1=4X(Ia)490.023X(Ia)190.02M_1=4X(Ia)_{\overline{49}|\,0.02}-3X(Ia)_{\overline{19}|\,0.02}

Compute

Compute

The two blocks give value factor 78.1729 and time-weighted factor 2,178.3542.

M1=2178.3542XM_1=2178.3542X

Answer

Answer

Their ratio is 27.87 years, corresponding to choice B.

DM=M1/PV=27.87(B)\boxed{D_M=M_1/PV=27.87\quad\text{(B)}}