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.
This approximation is 0.04% away from the true value of pi. While this approximation is accepted for most of its use in real life, the fraction is more accurate (giving about 3.14159292), and can be used when a value closer to pi is needed. Computers can be used to get better approximations of pi.