## Frank Morgan's Math Chat |

September 14, 1999

Is this correct?

**ANSWER.** Yes, 10 decibels is 10-fold, but that works only for 10, the base
of the decibel system. 20 decibels is 100-fold (10x10), and an increase of
5 decibels is an increase by a factor of the square root of 10.

Al Zimmermann (whose name we have been known to misspell without the double n) mentions that the basic unit is "a bel which is equal to 10 decibels. . . The bel was named after Alexander Graham Bell. (Dare I opine that someone accidentally left off one of the L's at the end of his name?)"

**NEW CHALLENGE** (Colin Adams). A web comment claims that, "If the population
of China walked past you in single file, the line would never end because
of the rate of reproduction." Is this true?

Send answers, comments, and new questions by email to
Frank.Morgan@williams.edu, to be eligible for *Flatland* and other book
awards. Winning answers will appear in the next Math Chat. Math Chat
appears on the first and third Thursdays of each month. Prof. Morgan's
homepage is at www.williams.edu/Mathematics/fmorgan.

Copyright 1999, Frank Morgan.