Derive the following approximation formula: %P DUR i 1 + i where %Pt = Pt+1Pt Pt and it = it+1 it. [Hint: Start from the formula P = n t=1 CPt (1+i)t . From there, calculate dP di . After that divide both sides by P and use again P = n t=1 CPt (1+i)t . Finally, apply the denition of duration: DUR = n t=1t CPt (1+i)t /n t=1 CPt (1+i)t to obtain the desired approximation formula. Note: this approximation would hold for i and P very small.]