The Lithuanian Informatics Olympiad is a problem solving contest for high school students. The work of each contestant is evaluated in terms of several criteria, where each criterion is measured according to its own scale (but the same scale for each contestant). Several jury members are involved in the evaluation. This paper analyses the problem how to calculate the aggregated score for whole submission in the above mentioned situation. The chosen methodology for solving this problem is Multiple Criteria Decision Analysis (MCDA). The outcome of this paper is the score aggregation method proposed to be applied in LitIO developed using MCDA approaches.