Ford Circles & Farey Sums

Simon Gregg, up to his usual tricks, is introducing fractions together with Ford circles, inspired by this Numberphile video with Francis Bonahon. This sketch lets you add two circles to get the circle in between tangent to both and the number line. There are many interesting properties! Thanks to Simon, Meagan Mutchmore, and Graeme Anshaw for great Twitter math talk!