Definition let ABC and D be four points is in a plane such that : (i)no three of them are collinear (ii) the line segments ABBCCD and DA do not intersect except at their and points.

Definition let ABC and D be four points in a plane that : ( i ) not three of them are collinear and (ii)the line segments ABBCCD and DA do not intersect except at the their endpoints.

There are 18 points in a plane such that no three of them are in the same line except five points which are collinear. The number of triangles formed by these points, is

There are 10 points in a plane and 4 of them are collinear. Find the number of straight lines joining any two of them.

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

How many different straight lines can be formed from 30 points in a plane? (no three points are collinear)

There are 15 points in a plane, no three of which are collinear. Find the number oif triangles formed by joining them.