Question
How many chords can be drawn through 21 points on a circle?
Solution
Since 21 points lie on the circumference of a circle.
∴ All the 21 points are distinct and no three of them are collinear. Now, we know that one and only one line can be drawn through 2 distinct points.
∴ Numbers of straight lines formed by 21 points by taking 2 at a time
Hence, the number of chords = 210.