=. Carlos the Curious took out a loan of $1,000 for one month. He always pays back his loans in
$1 bills. At the end of the month, when it comes time to pay, he lays out one thousand $1
bills on the table. He arranges them into ten equal piles, with one
hundred $1 bills in each
pile and he proclaims, "This is my principal." He then proceeds to
add five $1 bills to
each
pile, then says "and this is my interest."