Every student in a room is either a junior or a senior. There is at least one junior and at least one senior in the room. If 4/5 of the juniors is equal to 1/2 of the seniors, what fraction of the students in the room are juniors?
Pick one:  A) 13 / 20  B) 11 / 3  C) 5 / 13  D) 12 / 17  E) 17 / 20

Rationale: "let total number of juniors = j total number of seniors = s ( 4 / 5 ) j = ( 1 / 2 ) s = > s = 8 / 5 j total number of students = j + s = ( 13 / 5 ) j fraction of the students in the room are juniors = j / ( j + s ) = j / [ ( 13 / 5 ) j ] = 5 / 13 answer c"
Answer: C