Final answer:
The number of businesses in 2020 cannot be estimated without further information, specifically the start year for the formula An = 505 * 0.9^n. Calculating the equilibrium output in economic models requires algebraic manipulation, as demonstrated in the provided examples involving surges in investment and their impact on output.
Step-by-step explanation:
To estimate the number of businesses in 2020 using the provided formula An = 505 * 0.9^n, we need to determine the value of 'n' which represents the number of years since the start year. If we assume the start year is '0', and we consider 2020 to be 'n' years after, we can input the value of 'n' corresponding to 2020 into the formula to calculate the number of businesses.
However, further details are needed to calculate the value of 'n', such as the start year. Without this information, we cannot provide a numerical answer. In the case of growth models or economic models, the parameters are crucial to estimate outputs like the number of businesses or equilibrium output as in the scenario where investment rises to 500 and we calculate the equilibrium output using the provided equation. This calculation would require the application of algebraic manipulation to solve for Y, the equilibrium output.