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JAMB Mathematics 1981 Question 4

Question 4

Linear and Simultaneous Equations

Find a two-digit number such that three times the tens digit is 2 less than twice the units digit, and twice the number is 20 greater than the number obtained by reversing the digits.

  1. A.24
  2. B.42
  3. C.74
  4. D.47
  5. E.72
Show the answer and explanation

Answer: D (47)

Explanation

With tens digit x and units digit y: 3x = 2y − 2 and 2(10x + y) = 10y + x + 20, i.e. 19x − 8y = 20. Solving gives x = 4, y = 7, so the number is 47.