[ivanhoe]

Yes, but you presume that single worker working 40h/w will charge you the same hourly rate as the one working just 15h/week. It very much depends on peoples' own perception of how much work is "normal", and if you ask them to work more then the usual norm they'll probably ask to be better paid (per hour) for extra effort. Which would make them more expensive to hire, which would lead to hiring more 15h/w workers... some sort of equilibrium would surely arise, but only for jobs that are in high demand... unqualified workers will only work more and more...