3 ideas
A trick puzzle works by letting the solver add a constraint the wording never states, such as assuming pieces cannot be turned over, that lines must stay inside a boundary, or that a word has its usual meaning. The fix is to reread the question literally and ask what it actually forbids. Often the 'impossible' answer becomes easy once the imagined rule is dropped.
A flat figure can be cut into a small number of pieces and reassembled into a different figure with exactly the same area, for example turning a triangle or cross into a square. The challenge is to find the fewest cuts. The method is to match lengths: identify a segment in the target shape, such as the side of a square equal to the square root of the area, and place cuts so pieces carry that length across.
When equal distances are covered at different speeds, the average speed is not the arithmetic mean of the speeds. Slower legs take more time and so carry more weight. The correct figure is the harmonic mean, found by dividing total distance by total time, and it always falls below the naive average.