"Jeweils drei Mann waren in einer Gruppe vertreten."
Thank you very much, Christian, that explaines a lot. Still it is not applicable for 'man', is it?
Does anyone else think this could be translated, "Groups of three men each were represented"??
No. It refers to the fact that the men were represented in each group and not that the groups were represented by three men. Can you see the difference? However, it should definitely be men and not man.
Shouldn't it be 'Each of three men' rather then 'Each three men'? Also, despite the comments here, the suggested 'correct solution' I was given is 'Three man in each case were represented in a group'. I don't think 'Three man' can be right in any context.