Clock Math
The GeoGebra below shows a clock with N positions. Starting from the N o'clock, the system will draw lines each time jumping J hours ahead. 
1.  Consider N = 12. 
     (a)  What is the shape of the figure obtained when 
           (i)   J = 3?
           (ii)  J = 4?
           (iii) J = 6?
     (b)  Which value(s) of J will result in a complete cycle?
           [Hint: A complete cycle means the figure visits all the positions.]
     (c)  Which property must J have to result in a complete cycle?
2.  Try other values of N and J. See if your answer in question 1(c) is true.