I/Y = 8/2=4; FV = 100; N = 24; PMT = 0.05/2 x 100 = 2.50; PV = V0 = 77.13
I/Y = 7/2=3.50; FV = 100; N = 24; PMT = 0.05/2 x 100 = 2.50; PV = V- = 83.94
I/Y = 9/2=4.50; FV = 100; N = 24; PMT = 0.05/2 x 100 = 2.50; PV = V+ = 71.01
D = effective duration = (V- - V+)/2V0(Δy)
= (83.94-71)/(2x77.13x0.01)
= 8.38 years
