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    Question

    A number consists of two digits. The sum of the digits

    is 7. If 9 is subtracted from the number, its digits are interchanged. Find the number.
    A 43 Correct Answer Incorrect Answer
    B 48 Correct Answer Incorrect Answer
    C 52 Correct Answer Incorrect Answer
    D 54 Correct Answer Incorrect Answer

    Solution

    Let the ten’s digit be x. Then, unit digit = 7- x . No.= 10x + (7-x ) = 9x + 7 No. obtained by reversing the digits = 10(7- x ) + x = 70-9x (9x + 7) - 9 = 70- 9x , or, 9x + 9x = 70 - 7 + 9, or, 18x = 72 or x = 4, so ten’s digit = 4 and unit digit = 3 Hence, the required number = 43.

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