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      Question

      The sum of the digits of a two-digit number is 9. If 27

      is subtracted from the number, its digits switch their places. What is the number?
      A 63 Correct Answer Incorrect Answer
      B 56 Correct Answer Incorrect Answer
      C 70 Correct Answer Incorrect Answer
      D 65 Correct Answer Incorrect Answer

      Solution

      ATQ,

      Let the unit digit be 'a' and tens digit be 'b'.

      Original number = 10b + a

      Reversed number = 10a + b

      Given:

      a + b = 9 --------- (I)

      10b + a - 27 = 10a + b

      β‡’ 9b - 9a = 27

      β‡’ b - a = 3 --------- (II)

      Add equations (I) and (II):

      a + b + b - a = 9 + 3

      β‡’ 2b = 12 β‡’ b = 6

      Then a = 9 - 6 = 3

      Required number = 10 Γ— 6 + 3 = 63

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