ONE
    Númas
    ← Back to the programme
    OlympiadMediumNumber Theory7–9

    How many two-digit numbers are equal to seven times the sum of their digits?

    Quantos números de dois algarismos são iguais a sete vezes a soma dos seus algarismos?

    Answer options

    Solution

    Step 1 of 3

    1. 1.Write the number as 10a+b10a + b with aa from 11 to 99. The condition is 10a+b=7(a+b)10a + b = 7(a + b).