1. The problem statement, all variables and given/known data 1. Given n non-parallel lines such that no three intersect in a point, determine how many triangles are formed? 2. Given n lines in total, of which m are parallel, how many triangles are formed? 2. Relevant equations Combination nCr (n choose r) 3. The attempt at a solution for #1, its nC3, since the question is more like how many ways can we choose three lines from n lines. for #2, i am not sure. I assume since each parallel line adds a triangle, it would be m*(nC3). we would have m more triangles. I am not sure if this is correct, could any one please help?