Answer: a) The exponential function that describes the amount in the account after time t, in years, is given by:
A(t) = Pe^(rt)
where P is the initial amount invested, r is the annual interest rate (as a decimal), and e is the mathematical constant approximately equal to 2.71828.
Substituting the given values, we get:
A(t) = 19665e^(0.068t)
b) To find the balance after 1 year, we substitute t = 1 in the above formula:
A(1) = 19665e^(0.068*1) = $20,983.88
To find the balance after 2 years, we substitute t = 2:
A(2) = 19665e^(0.068*2) = $22,429.45
To find the balance after 5 years, we substitute t = 5:
A(5) = 19665e^(0.068*5) = $29,137.27
To find the balance after 10 years, we substitute t = 10:
A(10) = 19665e^(0.068*10) = $43,127.22
c) The doubling time can be found using the formula:
t = ln(2)/r
where ln is the natural logarithm function. Substituting the given values, we get:
t = ln(2)/0.068 ≈ 10.20 years
Therefore, the doubling time is approximately 10.20 years.
Explanation: