Usually solving such brain-teasers takes quite much time. Today we’ll tell you how to solve such puzzles using logic.
The thing is that such figures are called unicursal graphs and their special features can help the brain twister with simple counting.
Near each intersection write down the amount of lines crossing in this place. Any figures which have even amount of the crossing lines in each intersection could be drawn by the only line. Other figures should be drawn starting from an uneven intersection (the place where three, five or more line cross).
If the closed figure has less than two uneven intersections you should start the line in one of them and finish in another.
If the figure has more than two uneven intersections it’s impossible to draw such a figure without stopping.