The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 36. What is the difference between the two digits of the number ?

The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 36. What is the difference between the two digits of the number ? Correct Answer 4

Let the ten's digit be x and unit's digit be y
Then,
$$\eqalign{ & \Leftrightarrow \left( {10x + y} \right) - \left( {10y + x} \right) = 36 \cr & \Leftrightarrow 9\left( {x - y} \right) = 36 \cr & \Leftrightarrow x - y = 4 \cr} $$

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