Math CentralQuandaries & Queries


Question from pankaj, a student:

Q. There is 2 lines parallel to each other. If 1st has 5 points in it and 2nd 3 points in it, how many triangles can be formed?

Hi again Pankaj,

If the vertices of a triangle are three of the eight points on the two lines then exactly two of the vertices must be on the same line.

Select one of the two lines. Choose two points on this line. How many ways can you do that? These two points form the base of a triangle. Now choose one point on the second line. How many ways can you do that? Use the three points chosen to form a triangle. How many possible triangles are there constructed this way? Now select the second of the two lines and repeat the process.


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