Math Stinger # 135
by Steve Edwards, Professor of Mathematics

This time we have a counting, or combinatorics problem.
On a circle, pick an even number of distinct points and pair them up to draw chords.
How many ways can this be done for 3, 4, or (bonus question) any number of chords?
Consider two ways equivalent if the points can be pushed around the circle to transform
one into another without any point crossing another.  Consider two ways different
if the chords intersect in a different number of ways.  The two ways for the 2 chord case are
pictured.  Three ways for the 3 chord case are pictured.

Harder question:  what if all the points do not have to be distinct?

 

Send your solution  to sedwards@spsu.edu, or by snail mail to Steve Edwards in the Math 
Department.   The names of the first solvers will be posted here.

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