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    Question

    If '57x8y' is a five-digit number which is divisible by 72,

    then find the value of (5x - y).
    A 20 Correct Answer Incorrect Answer
    B -1 Correct Answer Incorrect Answer
    C 4 Correct Answer Incorrect Answer
    D -8 Correct Answer Incorrect Answer

    Solution

    ATQ,

    Since, 72 = 9 × 8

    So, the given number must be divisible by both 9 and 8.

    Divisibility by 8:

    Last three digits of the number (x8y) must be divisible by 8.

    For x = 1 and y = 6, the number "186" is divisible by 8.

    Divisibility by 9:

    Sum of the digits (5 + 7 + 1 + 8 + 6 = 27) must be divisible by 9, which it is.

    Hence, x = 1, y = 6

    And, 5x - y = 5 × 1 - 6 = 5 - 6 = -1

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