Henry Ernest Dudeney/Modern Puzzles/155 - Marking a Tennis Court/Solution

by : $155$

 * Marking a Tennis Court

Solution

 * Dudeney-Modern-Puzzles-155-solution.png

The $10$ labelled points are vertices of degree $3$, and therefore odd.

Hence we need to run over at least $4$ lines twice.

The shortest possible double tracking is running $BE$, $CD$, $GH$ and $FJ$ twice.

Hence the route to take:
 * $ADCDKGHGABEBCFJFEHK$

or its reverse.

There are minor variants:
 * By symmetry, $EH$, $AB$, $CF$ and $JK$ could be the lines to double track, then we start at $G$ and end at $D$, or the other way about
 * We could run over the double-tracked lines when we encounter the other end of them when we reach them, for example: $ADKGABCDCFEBEHGHJFJK$

and so on.