Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site stolaf.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!ihnp4!stolaf!gilje From: gilje@stolaf.UUCP (Mark A. Gilje) Newsgroups: net.puzzle Subject: SOLUTION to intersection puzzle! Message-ID: <1991@stolaf.UUCP> Date: Fri, 12-Oct-84 14:18:37 EDT Article-I.D.: stolaf.1991 Posted: Fri Oct 12 14:18:37 1984 Date-Received: Sat, 13-Oct-84 07:55:34 EDT Organization: St. Olaf College, Northfield MN Lines: 16 Here is the solution to the intersection puzzle. Sorry to post it so soon, but I'm going off the net for a while. For every four vertices in a polygon, there exists one and only one intersection when they are all connected. There are n choose 4 ways of choosing 4 vertices out of n vertices. Therefore, the maximum number of intersections in an n-gon is ......... n choose 4 or n(n-1)(n-2)(n-3)/24 for non-probablility experts. Thanks to those who sent answers! Mark Gilje stolaf!gilje