buy another 1

there was a brunette and a blonde walking home from school one day.the blonde looks at the floor and finds 2 quarters.the brunette then gets a great idea.she tells the blonde,"hey i'll sell you a great idea for a quarter." the blonde thinks to herself and decides to buy the great idea the brunette is selling.so,she hands her the quarter and asks,"what's your great idea?" the brunette anwers"buy another 1" the blonde then gives her the other quarter and asks again "ok,what's your other great idea?" the brunette then responds buy anther 1 and the blonde says "but i'm out of quarters"