CROSSING THE MOAT
You have discovered an old derelict house, with a square moat around it which is still full of water and about 3 metres across. Naturally, you want to get to the house, but even if you could take a run up and jump across the moat from this side, you would not be able to jump back.
However, you find two planks of wood which, when they are lowered across the moat, very nearly reach to the opposite bank – they are both just a few centimetres short. You would like to tie the planks together but you have nothing with which to tie them securely. How can you reach the derelict house by using the planks, and without getting your feet wet or being in danger of falling into the water?