Laws of Growth and Decay

Probably most of you know that the Laws of Growth and Decay are expressed
in 
the solution to the Differential Equation,

dy/dx = 1/x

I see an injustice in financial institutions for compounding interest on 
loans daily and compounding interest on savings annually, and raking in a 
fortune for the ignorant public.

I thought to add to their profits, there might be alternative equations to

sap out the consumer with mathematical rigmarole, such as,

(the money you have left) = 1/(the money you give them)^7

Many banks would like this arrangement.

Can you think of other more elusive, sophisticated terms?