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 can be the difference of X and Y ?
Choose the correct choice from the following options.
A) 73
B) 44
C) 33
D) 29
E) 9
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 E is a multiple of 9.   Answer: 9.
<result>E</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 can be the difference of X and Y ?