No, failing one subject (Science, Maths, SST) and having an additional subject won't result in the additional subject's marks replacing the failed subject's marks.In most boards (including CBSE), you need to secure the minimum passing marks (usually 33%) in each individual subject to pass the class, irrespective of additional subjects. Additional subjects are typically offered by students to improve their overall percentage or explore an extra field of interest. They don't function as replacements for mandatory subjects.
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