50:1 might barely work in an all-economy configuration, but few airlines (if any, outside special situations like sardine flights for Haj) fly all-economy configurations. You need a much higher ratio of flight attendants to passengers in premium classes. If a 300-passenger aircraft on an international route has 230 economy seats, 50 business class and 20 first, you'll need 5 FAs for J, about three for J and at least two for F. That's ten right there. These are rough figures, airlines differ in both aircraft configurations and staffing levels, but it supports the number in the original post.