r, b, and c are positive integers. If r, b, and c are assembled into the six-digit number rbcrbc, which one of the following must be a factor of rbcrbc? Answers
A) 16	B) 13	C) 5	D) 3	E) none of the above
Plug in some values and check -   rbcrbc = 123123   Not divisible by 16 and 5   let rbcrbc = 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 rbcrbc = 135135   Again divisible by 13   So, mark answer as (13) 13
<result>B</result>
r, b, and c are positive integers. If r, b, and c are assembled into the six-digit number rbcrbc, which one of the following must be a factor of rbcrbc?