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      Question

      On reversing its digits, a two-digit number becomes 78

      less than 180% of the original number. Also, the difference between the digits is 2 (tens digit larger). Find the original number.
      A 15 Correct Answer Incorrect Answer
      B 56 Correct Answer Incorrect Answer
      C 20 Correct Answer Incorrect Answer
      D 75 Correct Answer Incorrect Answer
      E None of these Correct Answer Incorrect Answer

      Solution

      Let tens = x, units = y. Original = 10x + y; swapped = 10y + x. 10y + x = 1.8(10x + y) βˆ’ 78 1.8 = 9/5 β‡’ multiply by 5: 50y + 5x = 90x + 9y βˆ’ 390 β‡’ 85x βˆ’ 41y = 390 … (I) x βˆ’ y = 2 … (II) β‡’ y = x βˆ’ 2 Substitute in (I): 85x βˆ’ 41(x βˆ’ 2) = 390 β‡’ 85x βˆ’ 41x + 82 = 390 β‡’ 44x = 308 β‡’ x = 7 y = 7 βˆ’ 2 = 5 Original number = 10Γ—7 + 5 = 75

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