Xeque,
Without wishing to divert the course of this forum,the number of C/C required is not dictated by no. of exits but by the number of pax that the aircraft is certified to carry. eg charter 757 capacity is 235pax Normal crew is 6-7 but can be reduced to 5 min,yet 757 has 8 exits.This leaves 3 exits uncovered.Works other way in that if you only had 3 pax on a flight you'd still require 5 Cabin Crew.