The CBSE Best 5 rule applies both to Standard X (AISSE), while the best 4 rule applies to Standard XII (AISSCE) examinations.
In Standard X examination, if a candidate takes an additional language or a subject (such as Home Science, IT, Commerce etc.), the aggregate of five subjects is the total of the marks in subjects where the candidate has scored the highest. The subject in which the candidate has scored the lowest is not taken into account. For example, if a candidate has scored 80 in English, 90 in Marathi, 70 in Science, 90 in Social Studies, 50 in Mathematics and 80 in Commerce (additional subject), the total percentage or the aggregate % will be calculated as :-
(Sum of best 5 subjects : English + Marathi + SST + Science + Commerce) ÷ 5
i.e. (80+90+70+90+80) ÷ 5 = 82 %.
Therefore your aggregate does not take Math into account since this is the subject where the candidate has scored the lowest.
I hope I have answered your question adequately.
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