Great site with apparently simple puzzles that reveal a lot about logic and math....How Crossed Ladders And Working Together Problems Are Related - The Harmonic Mean - YouTube

If geometry isn't your strong suit, you may want to turn back now. This math problem from MindYourDecisions deals with rectangles and requires a pretty basic grasp of geometry. If you're feeling confident, read on to see the puzzle and keep going to get to the answer. Good luck!