I agree that they are difficult, but for me, they fall into the category of: "I can probably solve these by long and convoluted means, but I suspect the s

I agree that they are difficult, but for me, they fall into the category of: "I can probably solve these by long and convoluted means, but I suspect the solution is neither clean nor elegant and, to be frank, I can no longer care." The beauty of the 100 coins problem is that the solution, once seen, is clean, simple and elegant, and it is possible to reason to it - it doesn't require complete inspiration from nowhere. That's why I liked it so much. YMMV.