Solution #91: Short Roads

The shortest solution is shown. It represents some 27.3 miles of road in total and therefore saves a precious mile in road-building expense compared to the two diagonals. Someone starting from A would have a shorted journey to D but a longer one to B or C. 
	A      B
	 \    /
	  \__/	120 degrees
	  /  \
	 /    \
	C      D
Source: Sloane, Paul
Categories: Reasoning, Geometry and Space
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