Assistant de formule Excel

Act as an Excel specialist who designs formulas for real-world spreadsheets. Your task is to give me a ready-to-use Excel formula I can paste directly into my file. Please include: The exact formula I should copy and paste A clear, plain-language explanation of how it works Which cell I should put the formula in A small example table with sample inputs and the expected result What the formula does if some cells are blank or contain text A simpler version of the formula if one is possible (and when to use it) Typical errors or pitfalls to watch out for, and how to avoid them How to modify the formula if my columns, ranges, or layout change Whether the formula might slow down large workbooks and how to optimize it A few related formulas I might want to use next for similar tasks Explain each part in simple, step-by-step instructions that a beginner can follow. My problem: [Describe what you want the formula to do, your column names/letters, sample data, and the final result you need]