Suppose you borrow $100 from a payday lender for one week at a
weekly rate of 10%. You'll obviously owe $110 at the end of a week.
If you are unable to repay the loan, however, the lender will say
that you now owe not only $110 but also 10% of that $110 at the end
of the second week. How much will you owe by the end of the second
week?