Passengers or seats?
Are the JAR requirements defined per passenger or per seat?
The US requirements seem to be 1 flight attendant per 50 seats irrespective of the number of passengers - so a 747 with 589 seats that happens to have 1 passenger aboard would need the minimum complement of 12 flight attendants.
Canada requires 1:40, and one country at least requires 1:36 - but at least in the case of 1:36, it is defined as 1 flight attendant per 36 passengers actually aboard, so that crew can be decreased in case of light loads.