3. Fermi estimation: hazards and risks In dealing with complicated questions with large uncertainties, critical thinking is important. Often, the challenge is to get a sense of about how large quantities are. A good approach is to consider the order of magnitudes involved. This process is sometimes called "Fermi estimation" after Nobel Prize winning physicist Enrico Fermi, who used to ask students on qualifying exams questions like "How many piano tuners are in Chicago?"

Activity 3.1: About much do Americans spend each year on Halloween? Estimate answers using only orders of magnitude

Activity 3.2 Estimate the order of magnitude - 1, 10, 100, or of the number of deaths per year in the U.S. caused by bears, sharks, bees, snakes, deer, horses, and dogs. A good way is to put them in the relative order you expect, and then try to estimate numerical values. For comparison, earthquakes cause about 20 deaths per year and severe weather causes about 500.

Activity 3.3: Making Memphis buildings more earthquake resistant Assume a large earthquake like those in would cause $10 billion of damage. If such an earthquake happens on average once in 500 years, estimate the annual damage (do all estimates to 1 significant digit). The benefit of strengthening the current building code would be reduced damage. If it were reduced by 50%, what would be the benefit? About $2 billion is spent on construction in the area every year. If strengthening the code added 3% to building costs, what would be the net increase ? For this simple estimate, which neglects some complexities on both sides, how do the costs and benefits compare?