
Dennis C. answered 07/27/21
GMAT Tutor with 15 years Experience and 99th Percentile Score
The key to answering this question (and doing so quickly) is to understand what information the question stem is giving us. In this case, if k has a factor, p, such that 1< p < k, then what the question is really asking us is: "is k a composite number?". The only way for k not to have a factor p that is between 1 and k is if k is prime.