Question

There are 20 non-collinear points in a plane. How many (a) straight lines (b) triangles can be drawn by joining these points?

Answer 1

There are 20 non-collinear points in the plane.

(a) We need to find the number of ways of drawing straight lines by joining these points.

Only two points are required to draw a unique line.

∴Number of ways of drawing a straight line

(b) We need to find the number of ways of drawing triangles by joining the given points.

Only three points are required to draw a unique triangle.

∴Number of ways of drawing a triangle