X and Y are positive two-digit integers such that the tens digit in X is the same as the units digit...

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 ?

Quiz

Answer/Solution

36

Steps/Work

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: C.