Not showing working — losing all marks for a correct answer when working is required
“we must stress the need to show working to maximise mark gaining potential. A simple arithmetic slip on a 3 or 4 mark question where the student shows no working can result in no marks being gained”— 4MA1 Paper 2F, June 2023
How to fix: Any question that says 'Show your working', 'Show clear algebraic working', or 'Show that...' requires every step to be visible. Write the formula first, then substitute numbers, then calculate. If your final answer is wrong, method marks are still awarded for correct steps. A correct answer without working where working is required scores zero. Never use trial and improvement for algebra questions.