If 20 lines are drawn in a plane such that no two of them are parallel and no three are concurrent, in how many points will they intersect each other?

Solution:

Let 0 be the number of intersection point of first line

Let 1 be the number of intersection point of 2nd line

Let (2+1) be the number of intersection point of 3rd line

Let (3+2+1) be the number of intersection point of 4th line

Let the no. of intersection point of line , in which