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.
small and accurate approximations, but approximations none the less. It's simplifying a great long (or endless) number (like pi) down to a smaller number with smaller characters, for example, if you were to use 3.14 as a standin for PI in a math problem, you're basically practicing floating point math.