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.
[math]\pi[/math] is approximately equal to [math]\frac{22}{7}[/math] but it is not equal to [math]\frac{n}{m}[/math] for any whole numbers [math]n,m[/math] because it was proved irrational in 1761.