Independent solution

How to solve this Geometric Annuity Exchange question

Setup

Setup

At time 5, the original perpetuity is worth 100/0.08 = 1,250. Move the replacement stream to that same date before comparing it.

V5=100/0.08=1250V_5=100/0.08=1250

Model

Model

Each replacement payment grows at the same 8% rate used for discounting. Consequently every discounted term has the same time-5 value X/1.08, and the 25-term sum is 25X/1.08.

1250=Xt=1251.08t1vt1250=X\sum_{t=1}^{25}1.08^{t-1}v^t

Compute

Compute

Equating 25X/1.08 to 1,250 gives X = 54. This cancellation is specific to equal growth and yield rates.

1250=X(25/1.08)X=541250=X(25/1.08)\Longrightarrow X=54

Answer

Answer

The calculation gives 54 for geometric annuity exchange, matching published choice A.

X=54(A)\boxed{X=54\quad\text{(A)}}