Consider an L-shaped ditch with straight sides and both legs of the same uniform width.
Part 1: How wide a ditch can be bridged with two 10 foot planks?
Part 2: How wide a ditch can be bridged with three 10 foot planks?
Note: consider the planks to be rigid line segments - very thin yet strong.
If the planks are rigid line segments, very thin yet strong, then they can be interleaved so that A is on B, B is on C, and C is on A. Instead of using the corner, place the free end of A and B on one side and the free end of C on the other. In theory, the free ends of A and B can be arbitrarily close, which means that we can bridge up to 20 feet.