Carcass wrote:
If XY represents a positive two-digit number, where X and Y are different digits, which of the following CANNOT be true?
A. X + Y = 9
B. (X)(Y) = 9
C. X – Y = 9
D. Y – X = 9
E. X/Y=9
Let's eliminate answer choices by finding values that satisfy 4 of the given equations..
A. X + Y = 9
If X = 4 and Y = 5, then X + Y = 9
ELIMINATE A
B. (X)(Y) = 9
If X = 1 and Y = 9, then (X)(Y) = 9
ELIMINATE B
C. X – Y = 9
If X = 9 and Y = 0, then X - Y = 9
Important: Recognize that the two-digit number here is 90ELIMINATE C
D. Y – X = 9
We may be tempted to use the values X = 0 and Y = 9 so that Y - X = 9. HOWEVER this would mean the two digit number is 09, which is a problem because 09 isn't technically a two-digit number, since 09 can be expressed as 9, a one-digit number
So, we'll keep answer choice D for now.
E. X/Y=9
If X = 9 and Y = 1, then X/Y = 9
ELIMINATE E
By the process of elimination, the answer is D