A fun geometry problem with frisbees – or technically two Discraft discs for the purists :)

Nearly three years ago I ran across this problem:

Two circles of the same size are tangent to each other in a plane. One of the circles stays fixed and the other circle rolls around the first circle one time. How many times does the rolling circle turn around its center?

A super fun, and easy to state problem. Here’s our first run through it (FamilyMath 23 – sheesh – we are over 250 now!!):


Well . . . today I ran across the same problem in our Introduction to Geometry book. Fun to see the ideas the the boys have 3 years later:


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