Chapter 06 – An Introduction to Macroeconomics
3. A mathematical approximation called the rule of 70 tells us that the number of years that it will
take something that is growing to double in size is approximately equal to the number 70 divided
by its percentage rate of growth. Thus, if Mexico’s real GDP per person is growing at 7 percent
per year, it will take about 10 years (= 70/ 7) to double. Apply the rule of 70 to solve the
following problem. Real GDP per person in Mexico in 2005 was about $11,000 per person, while
it was about $44,000 per person in the United States. If real GDP per person in Mexico grows at
the rate of 5 percent per year, about how long will it take Mexico’s real GDP per person to reach
the level that the United States was at in 2005? (Hint: How many times would Mexico’s 2005 real
GDP per person have to double to reach the United States’ 2005 real GDP per person?) LO2
Feedback: Using the rule of 70 Mexico’s Real GDP per person will double every 14
This implies that in 14 years Mexico’s Real GDP per person will be $22,000. This is still
only half of the $44,000 Real GDP per person in the United States.
4. Assume that a national restaurant firm called BBQ builds 10 new restaurants at a cost of $1
million per restaurant. It outfits each restaurant with an additional $200,000 of equipment and
furnishings. To help partially defray the cost of this expansion, BBQ issues and sells 200,000
shares of stock at $30 per share. What is the amount of economic investment that has resulted
from BBQ’s actions? How much purely financial investment took place? LO3
Feedback: Economic Investment is the purchase of buildings and machinery that can be
used to produce goods and services in the future. The restaurant firm builds 10 new
restaurants at a cost of $1 million each, which results in $10 million ($1 million x 10
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