Original practice · fully worked
Original variant: annual decrement inferred from a piecewise perpetuity price
A perpetuity pays 30 in each of years 1 through 5. Payments then decline by K each year for ten years; from year 16 onward they remain level at the year-15 amount. At a 5% annual yield, the price is 345.89. Calculate K.
- A
2.00 - B
2.10 - C
2.20 - D
2.30 - E
2.40
Answer and calculation
Valuing the first level block, the ten declining payments, and the level tail as functions of K gives a linear price equation. Solving it yields annual decrement 2.00, choice A.
Setup
Setup
Separate the five level payments from the ten-step declining block and the permanent level tail.
PV=30a5∣0.05+k=1∑10(30−kK)(1.05)−(5+k)+0.0530−10K(1.05)−15 Model
Model
Set the piecewise present value equal to the quoted market price.
345.89=PV(K) Compute
Compute
The resulting linear equation gives K = 2.000000.
K=2.00000000 Answer
Answer
The annual decrement is 2.00, selecting choice A.
K=2.00(A)