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    Question

    When the digits of a two-digit number are interchanged,

    the new number becomes 18 more than 125% of the original number. If the sum of the digits is 9, find the original number.
    A 72 Correct Answer Incorrect Answer
    B 54 Correct Answer Incorrect Answer
    C 36 Correct Answer Incorrect Answer
    D 63 Correct Answer Incorrect Answer
    E 27 Correct Answer Incorrect Answer

    Solution

    Let the unit digit and tens digit of the original number be тАШyтАЩ and тАШxтАЩ, respectively.
    Original number = (10x + y)

    According to the data given:┬а
    10y + x = 1.25 ├Ч (10x + y) + 18

    Multiplying both sides by 4,┬а
    40y + 4x = 50x + 5y + 72┬а
    тЗТ 46x тИТ 35y = тИТ72┬а тАж. (I)

    And, x + y = 9┬а тАж. (II)

    From (II), x = 9 тИТ y. Substitute in (I):┬а
    46(9 тИТ y) тИТ 35y = тИТ72┬а
    414 тИТ 81y = тИТ72┬а
    81y = 486┬а
    y = 6

    Then x = 9 тИТ 6 = 3.┬а
    So, original number = (10 ├Ч 3 + 6) = 36.

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