A. is a mathematical formula that is used to calculate the number of years it takes real gdp per capita or any other variable to increase by two hundred percent.
b. is a mathematical formula that is used to calculate the number of years it takes real gdp per capita or any other variable to double.
c. is a mathematical formula that is used to calculate the number of years it takes real gdp per capita or any other variable to quadruple.
d. states when an individual can be eligible for full social security benefits.