To solve this problem, we need to write a function that represents the value of an investment compounded continuously and determine the annual percentage yield (APY).
The formula for continuous compounding is given by:
\[ A(t) = P \cdot e^{rt} \]
where:
- \( A(t) \) is the amount of money accumulated after \( t \) years, including interest.
- \( P \) is the principal amount (initial investment), which is $920 in this case.
- \( r \) is the annual interest rate (as a decimal), which is 7% or 0.07.
- \( t \) is the time in years.
- \( e \) is the base of the natural logarithm, approximately equal to 2.71828.
Substituting the given values into the formula, we get:
\[ A(t) = 920 \cdot e^{0.07t} \]
Rounding the coefficients to four decimal places, the function becomes:
\[ f(t) = 920 \cdot e^{0.0700t} \]
The annual percentage yield (APY) for continuous compounding can be calculated using the formula:
\[ \text{APY} = e^r - 1 \]
Substituting \( r = 0.07 \):
\[ \text{APY} = e^{0.07} - 1 \]
Calculating this:
\[ e^{0.07} \approx 1.072508 \]
\[ \text{APY} = 1.072508 - 1 = 0.072508 \]
Converting this to a percentage and rounding to the nearest hundredth:
\[ \text{APY} \approx 7.25\% \]
The function representing the value of the account after \( t \) years is:
\[ f(t) = 920 \cdot e^{0.0700t} \]
The percentage of growth per year (APY) is approximately 7.25%.