A fifteen feet long ladder is placed across a street such that while its base is at one edge of the street its top rests against the opposite wall at a height of nine feet. Similarly, another ladder, twenty feet long, is placed resting across the other side-wall so that the two ladders cross each other. A spider wishing to cross the street, climbs up one ladder till it gets to the meeting point; thereafter, it climbs down the other.
How long will the spider take to accomplish the crossing assuming that he covers a foot in ten seconds?
If you assume that both ladders form right-triangles, and that the
twenty foot ladder rests at the base of the opposing wall, (the edge of
the street), then the point at which they cross would form the apex of
an equilateral triange. This means that all side are congruent, and
therefore 12 feet in length. The total distance crossed by the spider
would be 24 feet, and it would take him 240 seconds, or 4 minutes.