Symbiosis National Aptitude Test SNAP 2017 Paper

To construct 2 roads, three towns can be selected out of4 in 4 x 3 x 2 = 24 ways.
Now if the third road goes from the third town to the first town, a triangle is formed, and if it goes to the fourth town, a triangle is not formed. So, there are 24 ways to form a triangle and 24 ways of avoiding a triangle.