Okay, unless I'm reading this wrong, there is an inconsistency between these two questions?
On CAT #3, question #3 states:

"Is n/18 an integer?"
(1) 5n/18 is an integer
(2) 3n/18 is an integer

In the Number Properties Guide book on page 77, a very similar question states:

"If p is an integer, is p/18 an integer?"
(1) 5p/18 is an integer
(2) 6p/18 is an integer

As you can see, both questions and answers are very similar. CAT #3 says statement 1 is insufficient. However, in the guide book, it says statement 1 is sufficient. Let's take a step back and rephrase the question. "Are there two 3's and a 2 in p's prime box?" Looking at statement one, this should be sufficient, because there are (at least) two 3's and a 2 in p's prime box. Why does this guide book say statement one is sufficient, but exam #3 says it's insufficient??????

There is an important difference between the 2 questions. In your referred guide the question explicitly stated that 'p' is an integer. In the test qustion 'n' may need not be an integer. For the CAT question refer to the link below for explanation.

http://www.manhattangmat.com/forums/is-n-18-an-integer-1-5n-18-is-an-integer-2-3n-18-is-t636.html

Thank you

Thanks, Captain! Doing my work for me! :)