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    OlympiadMediumNumber Theory7–9

    How many times is the digit 77 written when all the whole numbers from 11 to 100100 are written out?

    Quantas vezes se escreve o algarismo 77 ao escrever todos os números inteiros de 11 a 100100?

    Answer options

    Solution

    Step 1 of 3

    1. 1.Count by position. As a units digit, 77 appears in 7,17,27,…,977, 17, 27, \ldots, 97: ten times.