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Unilorin Post-UTME Mathematics 2015 (Model questions) Question 25

Question 25

Linear and Simultaneous Equations

The sum of the digits of a two-digit number is 15. If the digits are interchange the number is increased by 9. Find the number

  1. A.78
  2. B.87
  3. C.97
  4. D.79
Show the answer and explanation

Answer: A (78)

Explanation

Swapping digits adds 9, so the units digit is 1 more than the tens digit: tens + units = 15 gives 7 and 8, so 78.