By far the most popular and well-stocked category of used instruments is our selection of guitars, where we've got a huge variety of all the big names. Used Gibson Les Paul, pre-owned Fender Telecaster and secondhand Stratocaster guitars are commonly found within these pages, waiting for their new homes with players and collectors.
22/7 is a pretty decent choice for teaching 11-year-olds about fractions that are close to pi. 355/113 would be better, if you think they can remember numbers that big. And approxRational is fun. Exercise for the interested reader: implement an inverse to approxRational.
In the sense of the question detail, pi can be written as a fraction, it is [math]\pi\over 1[/math]. So this is trivial; the usual related question is why pi cannot be written as a fraction of integers. x. This was proved in the late 18th century by Johan Heinrich Lambert.