Mathematicians call it the arithmetic of congruences. You can think of it as clock arithmetic. Temporarily replace the 12 on a clock face with 0. The 12 hours of the clock now read 0, 1, 2, 3, up to 11. If the time is eight oclock, and you add 9 hours, what do you get? Well, you get five oclock. So in this arithmetic, 8 + 9 = 5; or, as mathematicians say, 8 + 9 5 (mod 12), pronounced eight plus nine is congruent to five, modulo twelve.

About This Quote

More quotes by John Derbyshire, Prime Obsession: Bernhard Riemann and the Greatest Unsolved Problem in Mathematics

Related Quotes