Alternate Explanation of Question W-14

Question: How many triangles can be formed from a set of 8 points, where 5 of these points are collinear.

My Analogy: Since 5 points are collinear and 3 points randomly placed, then we can pick 2 points from the collinear part and 1 from random points. That means, 5C2*3C1/2!*1! + 1. Plus 1 because all the 3 random points can also form a triangle.

I need to know whether I am correct with this analogy or not. @Ishvinder

Hi Kaustubh,
Do note that we can pick two random points and the third one from that collinear set.

Oh yes, I forgot about this case. Then I think subtraction principle works well in this case