Original practice · fully worked
Original variant: modified duration of a three-date positive cash-flow stream
A portfolio pays 200 today, 300 at year 2, and 500 at year 5. At a 4% annual effective yield, calculate its modified duration.
- A
2.26 years - B
2.40 years - C
2.54 years - D
2.68 years - E
2.82 years
Answer and calculation
The portfolio price is 888.33. Dividing the negative price derivative 2509.18 by that price gives modified duration 2.8246 years, choice E.
Setup
Setup
Price the three cash flows at 4%; the time-0 cash flow is included in price but has no duration numerator.
P=200+300(1.04)−2+500(1.04)−5 Model
Model
Compute the negative derivative with respect to annual yield.
−P′(i)=2(300)(1.04)−3+5(500)(1.04)−6 Compute
Compute
The price is 888.330417 and derivative magnitude is 2509.184130, giving 2.82460679 years.
Dmod=P−P′(i)=2.8246067912 Answer
Answer
The modified duration is 2.8246 years, selecting choice E.
Dmod≈2.8246 years(E)