At an international conference, “Red” world countries and “Blue” world countries are the only participants. The ratio of “Red” world participants to “Blue” world participants is 7:3. If one-third of “Red” world participants are left-handed and two-thirds of “Blue” world participants are left-handed, then what is the fraction of the participants who are left-handed?
Options
A) 45 / 21 B) 46 / 2 C) 13 / 30 D) 23 / 6 E) 4 / 6

Rationale: "red : blue = 7 : 3 let red = 7 x and blue = 3 x 1 / 3 of red are left handed = > 1 / 3 * 7 x = 7 x / 3 red left handed 2 / 3 of blue are left handed = > 2 / 3 * 3 x = 6 x / 3 blue left handed fraction of participants who are left handed = total left handed / total participants = ( red left handed + blue left handed ) / total participants = ( 7 x / 3 + 6 x / 3 ) / ( 7 x + 3 x ) = 13 / 30 answer : c"
Answer: C