An Internet web site gives the current world population and projects the population for future years. Its projections for the number of people on Earth on January 1 in the years 2005 through 2009 are given in the table at right.
Population Projections
Year World population
2005 .............. 6,486,915,022
2006 ............. 6,581,251,218
2007 ............. 6,676,959,301
2008 ............. 6,774,059,223
2009 ............. 6,872,843,077
a. Find a recursive formula to model the population growth. What kind of sequence is this?
b. Predict the population on January 1, 2010.
c. In what year will the world's population exceed 10 billion?
d. Is this a realistic model that could predict world population in the next millennium? Explain.

The United Nations estimates that by 2025, the human population will increase by 31 percent. This diagram shows projected growth in the Western Hemisphere. Each square represents an increase of 1 million people. The outlined countries are Canada, the United States, Mexico, Colombia, and Brazil.

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