6.2. Mathematicians Andrey, Boris, and Viktor were solving problems from an olympiad. First, Andrey solved several problems, then Boris solved a third of the remaining problems. After this, a third of the problems remained unsolved, which Viktor completed. What part of all the problems did Andrey solve?
Solution. When Andrey solved several problems, Boris then solved a third of the remainder, and Victor, accordingly, two-thirds of the remainder. If this, according to the condition, is a third of all the problems, multiplying Victor's problems by three we get that twice the remainder after Andrey is the total number of problems in the Olympiad. That is, after Andrey, half of the problems in the Olympiad remained. Therefore, Andrey solved half of all the problems in the Olympiad.

Answer. $1 / 2$.