math problem

Question

Find the time it takes for $6,600 to double when invested at an annual interest rate of 19%, compounded continuously.

 

_______ years?

 

 

Find the time it takes for $660,000 to double when invested at an annual interest rate of 19%, compounded continuously.

 

________years?

 

Answer 1

A = Pe^rt, where 

a is the amount resulting, P is the principal, e is the math constant, r is the rate, t is the time in years

 

13200 = 6600e^.19t

2 =  e^.19t

 

t is between 3 and 4 years, but I'm not sure how to interpolate.