Question 1119812
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Any three points that are not collinear will form a triangle.<br>
If any number of points are placed on a circle, no three of them can be collinear.<br>
So you can form a triangle by choosing any 3 of the 15 points.  The number of ways to do that is "15 choose 3"
=(15*14*13)/(3*2*1) = 455