1998 CEMC Gauss (Grade 7) Problems/Problem 21
Problem
Ten points are spaced equally around a circle. How many different chords can be formed by joining any 2 of these points? (A chord is a straight line joining two points on the circumference of a circle.)
Solution
From each point, there are 9 other points that you could link it to. However, this accounts for each chord twice, so the answer is or