Chapter 9 Long-Run Economic gRowth S-123
3. The following table provides approximate statistics on per capita income levels
and growth rates for regions defined by income levels. According to the Rule
of 70, starting in 2015 the high-income countries are projected to double their
per capita GDP in approximately 70 years, in 2085. Throughout this question,
assume constant growth rates for each of the regions are equal to their average
value between 2000 and 2015.
Region
Real GDP per
capita (2015)
Average annual growth
rate of real GDP per
capita (2000–2015)
High-income countries $41,038 1.0%
Middle-income countries 4,584 4.4
Low-income countries 588 2.3
Data from: World Bank.
a. Calculate the ratio of per capita GDP in 2015 of the following:
i. Middle-income to high-income countries
b. Calculate the number of years it will take the low-income and middle-income
countries to double their per capita GDP.
c. Calculate the per capita GDP of each of the regions in 2085. (Hint: How many
times does their per capita GDP double in 70 years, the number of years from
2015 to 2085?)
3. a. i. The ratio of per capita GDP in 2015 of middle-income to high-income
countries is 0.112 or 11.2%.
ii. The ratio of per capita GDP in 2015 of low-income to high-income
countries is 0.014 or 1.4%.
b. Middle-income countries are projected to take 70/4.4 = 15.9, or approxi-
mately 16 years to double their per capita GDP, and low-income countries are
projected to take 30 years.
c. With a real GDP per capita growth rate of 1.0%, it will take 70/1 = 70 years for
GDP to double. Therefore, high-income countries are projected to double their
d. Using the projected per capita GDP figures in 2085, the percentages are as
follows:
i. Middle-income to high-income countries: 0.894 or 89.4%
e. Both the low-income countries and the middle-income countries (as defined
in 2015) have improved their per capita GDP relative to high-income countries