In order to calculate the number of Americans in 1990, we can use the following equation for exponential growth:
Where P is the final value after t years, P0 is the initial value and i is the growth rate per year.
So, using P0 = 2180000, i = 5% = 0.05 and t = 10, we have:
So the number of Americans in 1990 were 3,550,990.