The growth rate he needs to achieve his goal is approximatelly 19.8%
Step-by-step explanation:
Since the sum will be compounded continuously we have to use the appropriate formula given below:
M = C*e^(r*t)
Where "M" is the final amount, C is the initial amount, r is the interest rate and t is the time elapsed. Since Sung Lee will invest that sum at 18 years old and he wants to recieve the return at 25, then the time elapsed is given by 25 -18 = 7 years. We can now apply the data to the formula:
16000 = 4000*e^(r*7)
4000*e^(7*r) = 16000
e^(7*r) = 16000/4000 = 4
ln[e^(7*r)] = ln(4)
7*r = ln(4)
r = ln(4)/7 = 0.198
The rate of interest is given by (r)*100%, so we have (0.198)*100% = 19.8%.
