Final answer:
It will take approximately 14 years for the real GDP of a country to grow from $20 million to $80 million at an annual growth rate of 10 percent.
Step-by-step explanation:
To determine how long it will take for a country's real GDP to grow from $20 million to $80 million at a growth rate of 10 percent per year, we can use the formula for exponential growth:

In this case, we want to solve for the time (years) it will take for the real GDP to quadruple. Now, substituting the given values:
$80 million = $20 million ×


Using logarithms, we can solve for the number of years:
years = log(4) / log(1.10)
years ≈ 14.21
Therefore, it takes approximately 14 years for the real GDP to grow to $80 million.