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    OlympiadMediumLogic7–9

    Twelve cups stand upside down. One move turns over exactly 5 cups. What is the smallest number of moves after which all twelve can stand the right way up?

    Doze copos estão virados para baixo. Cada jogada vira exatamente 5 copos. Qual é o menor número de jogadas ao fim das quais os doze podem ficar todos virados para cima?

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    Solution

    Step 1 of 3

    1. 1.Each cup must be turned an odd number of times, so the total number of turns is a sum of twelve odd numbers, which is even. Each move contributes 5 turns, so 5m must be even and m is even.