Using continuous compounding, it is found that Sandra's account pays an interest rate of 8.4%.
The amount of money, in continuous compounding, after t years, is given by:
[tex]A(t) = A(0)e^{kt}[/tex]
In which:
In this problem, Arnold's earnings are given by:
[tex]A_A(t) = Pe^{0.08t}[/tex]
Sandra earns [tex]e^{0.004t}[/tex] times the amount Arnold earned in the same time, hence:
[tex]A_S(t) = e^{0.004t} \times Pe^{0.08t} = Pe^{(0.08 + 0.004)t} = Pe^{0.084t}[/tex]
Comparing to the standard equation, Sandra's account pays an interest rate of 8.4%.
To learn more about continuous compounding, you can take a look at https://brainly.com/question/24722580