| I teach a Quantitative Methods course and in it, I have students read through the Guesstimation book by Weinstein and Adams (listed on that wiki page). There is also a second volume. They do 11 blog entries each on modifying a question from each chapter and then computing it out. I also have them watch TED talks and come up with guesstimation critiques of the talks, also in the form of 11 blog entries. These are highly effective exercises. I recommend doing something similar. If you can, find some others who are interested in doing the same. Reading each other's questions and answers is very valuable in detecting mistakes and comparing your own technique to theirs. Fundamentally, you just have to do it. The mental facts needed to memorize are surprisingly minimal. The Guesstimation book lists some good suggested ones. Often you will find you already have some sense of a number. By taking reasonable boundaries on either end of the plausible range and then taking the geometric mean, you can get a decent approximation. The mental math is also fairly minimal. It just requires two digit arithmetic for the most part along with being comfortable with powers of 10. There are books on mental math, but I think practice is sufficient for two digits: http://arithmetic.zetamac.com |