Math: Combinations

There are 20 points all in one straight line and 15 others in a parallel line. How many possible triangles having these points as vertices can be formed?

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asked by Jesse

  1. I can form a triangle by choosing any two points on the one line, then one of the points from the other line.
    so the number of ways
    = C(20,2)x15 + C(15,2)x20
    = 2850 + 2100
    = 4950

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    posted by Reiny

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