views:

59

answers:

4

With a back-of-the-envelope calculation you can mentally obtain an answer to a question, within an order of magnitude of its actual value. Some shortcuts can simplify these calculations. In computing I've found the rule

103n is-close-to 210n

invaluable. For instance, through this I can say that I can binary search through a billion records with about 30 operations. What other shortcuts do you use and recommend? Let's put them all here and vote your favorites.

A: 

103n is-close-to 210n

Diomidis Spinellis
A: 

Light travels at one foot per nanosecond

Diomidis Spinellis
A: 

pi seconds is a nanocentury

Diomidis Spinellis
A: 

G ~10 m/(s2)
Dimensional Analysis
Rounding (simple, yet effective)

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