Question

You want to make an investment in a continuously compounding account earning 12.6% interest. How many years will it take for your investment to double in value? Round the natural log value to the nearest thousandth. Round the answer to the nearest year.
I got 5 years

Answer 1

2 = e^(.126 t)

ln(2) = .126 t

5.501... , should round up

Answer 2

P = Po*e^rt = 2Po.
Po*e^rt = 2Po,
e^rt = 2,
rt*Lne = Ln2,
rt = Ln2/Lne,
r*t = 0.69,
t = 0.69/0.126 = 5.5 yrs.