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Not showing working — writing only the final answer, especially in multi-step and 'show that' questions
“The inclusion of working out to support answers is essential to gain full credit but remains an issue for many. Working out not only needs to be shown, it also needs to be shown in a clear and logical way, demonstrating the processes of calculation used.”— 1MA1 Paper 2F, June 2023
How to fix: Write every step: formula → substitution → calculation → answer. On calculator papers, still write down the numerator and denominator separately before dividing. For 'show that' questions, show each algebraic step explicitly — examiners award method marks for each correct line, not just the final result.