An estimate is not a guess. It is the result of a rational procedure.

Learning objective Make models using imagination and three techniques:

• Make oversimplifying assumptions
• Break big problems into smaller problems
• Make estimates or even guesses to solve the smaller problems.

Some tips

• Ask: “What information would help me solve the problem?”
• Use rough data from readily available sources
• When in doubt, guess to nearest power of ten (logarithmic scale)

Before class

• Watch Powers of Ten
• Find out who Enrico Fermi was
• Read about the famous problem of the number of piano tuners in Chicago
• See how a Fermi problem can be tackled.
• Consult the main points of the lesson

In class

• Solve some Fermi problems, working in groups
• Orientation to project with Keeling’s Mauna Loa atmospheric CO2 data.
• Start R Chapter 3 on fitting models to data (pages 38-39, the utilities data).