Whenever I'm evangelizing the PPACA, I always hit on the regulations around the MLR - the "medical loss ratio", ie, what percentage of premiums are paid back out as medical claims.

One insurance company had a plan with a ten-percent MLR! (Marketing plans that didn't cover anything to college kids, of course.) They took in premiums and kept ninety-percent of it as profit.

My comment was just on how APR is calculated for short term loans.

Also, you only double your money every 3 months if none of your loans default and you collect everything. Most of these loans default. Profits are way slimmer than you're imagining, even for the scammers (Who I definitely agree should be punished for these practices).