q, b, and c are positive integers. If q, b, and c are assembled into the six-digit number qbcqbc, which one of the following must be a factor of qbcqbc?  Choose the correct choice from the following answers.
A) 16  B) 13  C) 5  D) 3  E) none of the above
Plug in some values and check -   qbcqbc = 123123   Not divisible by 16 and 5   let qbcqbc = 125125   Not divisible by 3   Only option (B) and (E) is left in both the cases...   Check once more to marke (13) as correct answer   let qbcqbc = 135135   Again divisible by 13   So, mark answer as (13) 13
<result>B</result>
q, b, and c are positive integers. If q, b, and c are assembled into the six-digit number qbcqbc, which one of the following must be a factor of qbcqbc?