Official Solution:Is a two digit positive integer \(xy\), where \(x\) is the tens digit and \(y\) is the units digits, even? Notice that the question asks whether \(y\), the units digit of a two digit positive integer \(xy\), is even.
(1) \(x\) is an even number. Clearly insufficient.
(2) The greatest common factor of \(x\) and \(y\) is 1
Also, insufficient. For example, consider 12 and 13.
(1)+(2) Both \(x\) and \(y\) cannot be even because in this case the greatest common factor of \(x\) and \(y\) would not be 1 (as given in the second statement), thus \(y\) is odd. Sufficient.
Answer: C