Guesstimation, or The City in the Sky

On average, how many people are airborne over the US at any given moment?

That’s a typical question from the new Princeton University Press book by Lawrence Weinstein and John Adam.  The title is Guesstimation and the subtitle is: Solving the World’s Problems on the Back of a Cocktail Napkin.

What’s your guess and why; let us know in the comments and I’ll post their answer later today.  The book also tackles such hoary chestnuts as "How many piano tuners are there in Los Angeles," although for mysterious reasons (are they mostly part-timers?) they fall far short of the actual number in the L.A. Yellow Pages.

This book isn’t for everyone but if you think you might like it you probably will.

Addendum: I post the authors’ answer at about comment #31.