for exmple, i solved a problem when its rank was 300, and now its one is 200. does it mean that my rank decreased for 100???

The problem difficulty is calculated by the formula depending on the number of authors who have solved it and the age of the problem. The fewer new authors solve the problem per unit of time, the greater the difficulty. The difficulties of all problems are updated every night. Author rating is the sum of the difficulties of all his solved problems from the archive.