Juud,
On a 3-class 777, we have 5 crew to 240 pax (traveller and traveller +). One is a Purser running the galley, 4 main crew in the cabin delivering drink/food etc. Some people will think it's easy being in the galley (doing "nothing", but if the Purser does the job properly, there is plenty to do)
On 737 with 147 pax, we regularly have 3 crew (one Purser and 2 Main crew). Purser is required in the cabin.
This is from LGW.
Hope this clarifies.
Gg