Original practice · fully worked
Original variant: growth rate implied by a perpetuity price
A monthly perpetuity pays 400 for the first twelve months. At the start of each later twelve-payment block, the monthly amount increases by annual rate g. Its present value is 100,000 at a 6% annual effective yield. Determine g.
- A
0.50% - B
0.82% - C
1.07% - D
1.35% - E
1.60%
Answer and calculation
The first monthly block is worth 4651.52. Solving the geometric block-price equation gives annual step growth 1.0694%, choice C.
Setup
Setup
Price the first twelve payments at the exact monthly equivalent of 6%.
j=1.061/12−1 B=400a12∣j=4,651.5201 Model
Model
Successive block values form a geometric series with ratio one plus g divided by 1.06.
100,000=1−(1+g)/1.06B Compute
Compute
Rearrange for the annual step growth.
g=1.06(1−100,000B)−1=0.0106939 Answer
Answer
The block growth rate is 1.07%, choice C.
g≈1.07%(C)