Original practice · fully worked
Original variant: accumulated interest separate from principal
An investor deposits 500 at each year-end for 12 years. Each deposit earns 5% annually, but every year's interest is withdrawn immediately and reinvested at 2% until year 12. Determine the year-12 value attributable only to reinvested interest, excluding the 6,000 principal.
- A
1,284.60 - B
1,512.48 - C
1,765.11 - D
2,041.77 - E
2,315.60
Answer and calculation
At each year-end the prior deposits generate 25 each. Accumulating the resulting triangular interest stream at 2% gives 1765.11, choice C.
Setup
Setup
Each completed deposit-year produces 25 of withdrawn interest.
500(0.05)=25 Model
Model
At year m+1, m prior deposits produce 25m; carry that amount to year 12 at 2%.
I12=25m=1∑11m(1.02)11−m Compute
Compute
Evaluate the eleven interest installments.
I12=1,765.1122 Answer
Answer
Reinvested interest alone is 1765.11, choice C.
I12=1,765.11(C)