Independent solution

How to solve this Discrete Crediting Date question

Setup

Setup

Write both accounts’ values after t years using their actual crediting periods: two credits per year for one account and twelve for the other.

1000(1.03)2t=2000(1.0025)12t1000(1.03)^{2t}=2000(1.0025)^{12t}

Model

Model

Solving the continuous equality gives t = 23.775 years, or 285.3 months. Equality is only realized when both accounts have reached an applicable crediting date.

t=ln22ln1.0312ln1.0025=23.775 yearst=\frac{\ln2}{2\ln1.03-12\ln1.0025}=23.775\text{ years}

Compute

Compute

The next common semiannual boundary is month 288, not month 285 or 286. Thus the discrete answer is 288 months.

12t=285.3,next semiannual credit date=28812t=285.3,\quad\text{next semiannual credit date}=288

Answer

Answer

The calculation gives 288 for discrete crediting date, matching published choice E.

n=288 months(E)\boxed{n=288\text{ months}\quad\text{(E)}}