Top 10 Mark-Losing Mistakes in DSE Maths (and How to Fix Them)

Most lost marks have nothing to do with difficulty — they're the same traps, repeated. Here are the 10 highest-frequency mark losers in HKDSE Maths.

1. Missing / wrong units (u-1) — deducted once per paper, but lost every year. Always add units.
2. Wrong precision (pp-1) — they ask for 3 significant figures, you give 2. Read the requirement.
3. Sign error when completing the square — the constant term's sign is the usual culprit; verify by substituting back.
4. Ignoring domain / range — log, square-root and zero-denominator restrictions get dropped.
5. Missing trig solutions — losing a quadrant when solving trig equations.
6. Not flipping the inequality when multiplying by a negative.
7. Forgetting "without replacement" in probability — the condition changes the answer.
8. Unlabelled key points on graphs — intercepts, vertices, asymptotes left unmarked lose points.
9. Skipping steps — mental jumps leave the marker no M mark to award.
10. Poor time allocation — stuck on one hard item, no time for easy marks.

Fixing it systematically

A checklist helps, but it's more effective to let the system track which objectives you lose marks on. In DSE ScoreCoach, every grade records which step cost you, building your personal mark-loss ranking — not a vague "weak at algebra" but the specific action "sign when completing the square". Drill that a few times and the leak is sealed.

In your final two weeks, print these 10 and tick them off after every paper. Most score gains come from losing fewer marks.