Posted by **Jesse** on Wednesday, March 4, 2009 at 4:09pm.

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?

- Math: Combinations -
**Reiny**, Wednesday, March 4, 2009 at 5:15pm
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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