Where students lose marks — and exactly what to do about it

Who this is for, and how to use it

For Class 10 and Class 12 students preparing for pre-boards or the board exam, and for teachers planning revision lessons. CBSE marking schemes give marks for each step, not just the answer. So several of the mistakes ranked here cost a mark or two inside a question you could otherwise do: a skipped step, a sign slip, a forgotten + C, or a radius that was not squared.

Next step: sit one full paper under exam conditions, then go through it against your class’s list and count the marks each mistake cost you. Our free sample papers follow the board pattern and need no sign-up: Class 10 sample paper 1 or Class 12 sample paper 1.

Choose your course

Each page: the top mistakes with fixes and worked examples, a topic trend table and a per-paper view where we have mapped the papers, and what to focus on next (clearly labelled as prediction).

The two mistakes that cost the most marks, course by course

The first two on each course page, ordered by how often and how widely they were reported, with the fix in one line. The course page has the worked examples and the rest of the list.

CBSE Class 10 Maths

• Skipping steps the marking scheme rewards. Show the formula, the substitution and the simplification on separate lines, even when you can do it mentally.
• Sign and arithmetic slips. Bracket negatives when substituting; re-check each line; leave a few minutes to recheck calculations.

CBSE Class 12 Maths

• Integration: + C forgotten and substitution signs. Write + C on every indefinite integral; show the substitution and dt line.
• Partial fractions for repeated or quadratic factors. Repeated (x − a)² needs A/(x − a) + B/(x − a)²; an irreducible quadratic needs (Bx + C)/(x² + …).