Original practice · fully worked
Original variant: scale deposits to buy a target perpetuity
Deposits of 100q, 150q, and 200q are made at times 0, 1, and 2 into a fund earning 8% annually. At time 6 the fund buys a perpetuity-immediate paying 120 every half-year, valued at a 10% annual effective yield. Determine q.
- A
3.20 - B
3.48 - C
3.78 - D
4.05 - E
4.32
Answer and calculation
The perpetuity requires 2458.57 at time 6, while the unscaled deposits accumulate to 651.18. Their ratio is q = 3.7755, choice C.
Setup
Setup
Find the half-year rate and the fund required for the perpetuity.
j=(1.10)1/2−1 F6=j120=2,458.5706 Model
Model
Accumulate one unit of the stated deposit pattern to time 6.
B=100(1.08)6+150(1.08)5+200(1.08)4=651.1844 Compute
Compute
The actual accumulated deposits equal q times this base value.
q=651.18442,458.5706=3.7755365 Answer
Answer
The deposit scale is 3.78, choice C.
q≈3.78(C)