The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 81. What is the difference between the two digits of that number?
Choose the correct option:	A) 4	B) 5	C) 6	D) 8	E) 9
Sol.   Let the ten’s digit be x and unit’s digit be y,   Then, (10x + y) - (10y + x) = 81 ⇔ 9 (x - y) = 81   ⇔ x - y = 9   Answer 9
<result>E</result>
The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 81. What is the difference between the two digits of that number?