The sum of the digits of a two-digit number is 12, and the difference between the number and the number obtained by interchanging the two digits of the number is 18. Find the number.

• A. 12.5
• B. 25
• C. 75
• D. 50

Answer: (C)

Let the number be 10x + y.∴ x + y = 12    ...........(i)10x + y - (10x + x) = 18or 10x + y - 10y - x = 18or 9x - 9y = 18∴ x - y = 2From (i) and (ii), x = 7, y = 5∴ Number = 75