A perpetuity costs 77.1 and makes annual payments at the end of the year. The perpetuity pays 1 at the end of year 2, 2 at the end of year 3, ..., n at the end of year (n+1). After year (n+1), the payments remain constant at n. the annual effective interest rate is 10.5%. Calculate n.
(A) 17 (B) 18 (C) 19 (D) 20 (E) 21
PV = v[(Ia)_{n|}] + v^{n+1} * n/i = v[ (ä_{n|} - nv^n) / i ] + v^{n+1} * n/i = (v ä_{n|}) / i = a_{n|} / i = (a_{n|.105}) / .105 = 77.1, a_{n|.105} = 8.0955
(1 - v^n) / i = 8.0955, 1 - v^n = 0.105 * 8.0955 = 0.8500275, v^n = 0.1499725, -n * ln 1.105 = ln 0.1499725,
n = - (ln 0.1499725) / (ln 1.105) = 19.002
Alternatively: PV = -8.0955, I/Y = 10.5, PMT = 1, CPT N = 19 Answer: C.