Question

How many chords can be drawn through 21 points on a circle?

Answer 1

Solution:
A chord can be drawn by joining any two points on a circle. Therefore, the number of chords that can be drawn out of 21 points is ²¹C₂, which is given by 

²¹C₂ = 21! / 2!19! = 21*20*19! / 2*19! = 210

Thus, the number of chords is 210.