The inspector need only travel nineteen miles if he starts at B and takes the following route: BADGDEFIFCBEHKLIHGJK. Thus the only portions of line travelled over twice are the two sections D to G and F to I. Of course, the route may be varied, but it cannot be shortened.
242.--THE TUBE INSPECTOR'S PUZZLE.
From Amusements in Mathematics by Henry Ernest Dudeney.
