Colegiul National B.P. Hasdeu (Buzau, Roumanie)
We treated all the 3 element subsets as a string of subsets, then used properties of strings (general term, ratios, etc) to determine the maximum ratio between the numbers, the number of subsets for each ratio, and, eventually, the total number of 3 element good sequences. same for point b), but with 10 element subsets. we will finish our problem on saturday and we will explain how we thought of points c and d then.