The Mathematical Sciences Research Institute of Berkeley is putting a series of puzzles on Muni buses in San Francisco, one puzzle a month from October to February.

There will be $100 prizes for people who solve them, the winner to be drawn from a pool of correct answers submitted. Answers will be submitted by computer and available to the public on the MSRI Web site when that month's contest is over.

This is an attempt to "enliven the daily commute,'' says MSRI, "and offer riders a way to experience some of the excitement of mathematics.'' Commuters not interested in math can stick with experiencing the familiar Muni mix of psychology, sociology and body odor.