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.
Mnemonic Techniques for Numbers. Mnemonics for the number Pi. Pi is the ratio between a circle's circumference and its diameter. When expressed decimally it extends to infinity as a series of apparently random digits. It is useful to scientists to know approximately the value of pi, perhaps to two or three decimal places.