The Castle Moat
Sir Lancelot with his squire Jerkin wants to rescue the lovely princess Jennivere, kept prisoner by the Black Knight in his impregnable castle.
His obstacle is a rectangular moat full of poisonous dragon fish.
Looking about for useful resources, Jerkin finds two planks each of which is exactly as long at the moat is wide.
How will they get across without falling into the moat?