π is defined as the ratio of the circumference of a circle to its diameter

- of course π is an irrational number, thus it cannot be exactly written as a fraction

π is appr 3.1415926...

A fraction which has been used for an approximation for π for a long time is 22/7

A much better one is 355/113, quite easy to memorize because of its nice symmetry.

Today's calculators have π as a build-in constant and we no longer need that 22/7, which contains a significant error