Difference between a two-digit number and the number obtained by interchanging…

For any two-digit number with tens digit x and units digit y, the number equals 10x + y. Reversing its digits gives 10y + x, and the difference between the number and its reverse is always 9(x − y) — nine times the difference between the two digits.

1. Let the tens digit be x and the units digit be y, so the original number is 10x + y and the number formed by interchanging the digits is 10y + x.

2. Difference: (10x + y) − (10y + x) = 9x − 9y = 9(x − y).

3. This difference is given as 36, so 9(x − y) = 36, which gives x − y = 4.

Cross-check: digits differing by 4, e.g. 51 and 15, give 51 − 15 = 36, confirming the difference between the two digits is 4.