X and Y are positive two-digit integers such that the tens digit in X is the same as the units digit in Y, and the units digit in X is the same as the tens digit in Y. Which of the following could be the difference of X and Y ? Choose the most appropriate option
A) 73 B) 44 C) 36 D) 29 E) 8
X and Y are positive two-digit integers such that the tens digit in X is the same as the units digit in Y, and the units digit in X is the same as the tens digit in Y:   X = 10a + b   Y = 10a + b   X - Y = (10a + b) - (10a + b) = 9(a - b). As you can see the difference must be a multiple of 9. Only option C is a multiple of 9.   Answer: 36.
<result>C</result>
X and Y are positive two-digit integers such that the tens digit in X is the same as the units digit in Y, and the units digit in X is the same as the tens digit in Y. Which of the following could be the difference of X and Y ?