Problem:
Two points are selected independently and uniformly at random inside a regular hexagon. Compute the probability that a line passing through both of the points intersects a pair of opposite edges of the hexagon.
Solution
Solution:
First, we compute the probability that the line through two random points in a triangle passes through segments and . We can take an affine transform of the two random points and the triangle such that becomes equilateral. Since the distribution of the two points is still uniform and independent, the probability of the line intersecting any two given sides is by symmetry.
Next, we compute the probability that the line through two random points in a rectangle passes through opposite edges and .
If the line passes through and , the points must both lie in triangle , whose area is half that of . Given this, the probability the line passes through those two sides is , as computed before. Thus the probability the line passes through and is . The same goes for the other pairs of adjacent edges. By symmetry, the line is equally likely to pass through either pair of opposite edges, each with probability .

We now return to the original problem. If the line passes through a pair of opposite edges, then both points must be in the rectangle formed by these edges, which has area that of the hexagon. Given this, the probability the line passes through those two edges is as computed before. Thus, the probability that the line passes through the given pair of opposite edges is . Hence, the probability the line passes through any of the three pairs of opposite edges is .