Question 1013066
You have 15 points that are connected with 14 other points with a straight line.
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Notice the problem doesn't say that each point reaches out to touch every other point, it says each point is connected to every other point. This means that if I have two points connected by a line, A and B, I only need one line to connect the points.
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So, for every point to reach out to every other point you'd need:
15*14= 210 lines
But as I said, once you connect two points with one line, well, they are connected. So you only need:
210/2= 105