World in the Balance
 
Student Handout

Double Up
"At first there is only one lily pad in the pond, but the next day it doubles,
and thereafter each of its descendants doubles. The pond completely fills up
with lily pads in 30 days. When is the pond exactly half full? Answer: on the
29th day."—Old French riddle
Unlike the lily pads in the French riddle, the human population does not double
in size every day. However, it is increasing more quickly than you might
suspect. In this activity, you will have the chance to investigate how quickly
the populations in different countries are increasing.
Procedure
Your team will be assigned six to eight countries. Find each country's
10year growth rates on the "Growth Rates Worldwide" handout. (The 10year
growth rate tells you the rate at which the population of the country increases
every 10 years.)
Based on each country's growth rate, make a prediction as to how many
decades (10year periods) it might take for each country's population to double
in size. Record your predictions on a separate sheet of paper.
Use an initial population of 50 individuals for each country. Follow the
steps listed on your "Calculating Population Growth" handout to calculate how
large each country's population will be after 10 years. Record the new
population size on a separate sheet of paper.
Repeat the process until each country's population size doubles.
Use your results to make a graph that shows how the population for each
country increases over 10year periods. Graph the number of years on the xaxis
and the number of people on the yaxis. Draw the bestfit curve.
Questions
Write your answers on a separate sheet of paper.
Compare your results with your original predictions. How do they compare?
Compare your results with those of other teams. How does increasing or decreasing the growth rate affect how quickly the population size increases or decreases?
Use your "Growth Rates Worldwide" handouts to find the country or territory
with the lowest growth rate and the country or territory with the highest
growth rate. Use your formula to calculate how long it would take each one to
double. How do they compare to the countries in your original data set? If you
were a leader of either of those countries, what would be your concerns about
your country's growth rate?
The world population is currently estimated at roughly six billion people.
If the projected 10year growth rate is 0.123, how long will it take for the
world population to double?
