Consider the 5 points comprising of vertices of a square and the intersection point of its diagonals. Then the number of triangles that can be formed using these points are
To form a triangle, 3 points out of 5 can be chosen in 5C3=10 ways.
But out of these, the three points lying on the 2 diagonals will be collinear.
∴ 10−2=8 triangles can be formed