The plates must touch the edge of the table, so their centers must lie on the circle with radius R - r (see the figure).
1 | 2 | 3 | 4 | |
{1} | - | 1 | 1 | 1 |
{1, 2} | 2 | 1 | 1 | 1 |
{3, 1, 2} | 3 | 3 | 1 | 3 |
{3, 1, 2, 4} | 3 | 3 | 1 | 3 |
In conclusion, a couple of words about the difficulty order in the problemset must be said. Difficulty of a problem is subjective. Especially if we need to compare a problem with idea and nearly without implementation and implementation without idea. As a result, different participants form different preference lists (russian). I can't deny that the order chosen during preparation of the contest appeared to be inadequate with the number of solutions for the problems, and it surely can be not liked by someone personally. Nevertheless, I want to say a couple of words in its support. Namely, about principles we have used to choose it.