Error-spotting gives you a plausible proof and asks for the first line that does not follow. Verify each line using only the lines above it — never the conclusion you want. Recurring culprits: division by a possibly-zero expression, square roots without ±, converse-for-contrapositive swaps, examples posing as general proof, and quantifier scope slips.
Stop at the first unjustified line even if later lines look worse — the question asks for the first break. Train slowly untimed first; speed comes from pattern recognition, not skimming.
Study method: attempt five timed questions, log every miss with its topic code, redo misses from scratch within 48 hours, then re-attempt the topic a week later. Pair each hub with its drill link below and a fortnightly full mock.
Place this topic in the wider test with the syllabus checklist and Paper 1 vs Paper 2, learn the timing system in how to prepare, and check what scores mean in scores explained.