Acostumer buys 17.01 in gas and requests one five dollar ticket, two one dollar tickets, and one three dollar ticket. he gives you two winning tickets to be redeemed: five dollar and the other for two dollars. how much change would he recieve from 100 dollar bill?

The customer gives you:
-- a  ticket worth . . . . . . 5
-- a ticket worth. . . . . . . 2
-- a bill. . . . . . . . . . . . 100
              
-- Total. . . . . . . . . . . . 107

You give the customer:
-- gas worth . . . . . . . . 17.01               
-- a ticket worth . . . . . . 5
-- two $1 tickets worth . 2
-- a ticket worth . . . . . . 3
           
-- Total . . . . . . . . . . . . 27.01

In order to make the trade even, you owe the customer

                               (107.00  -  27.01)  =  $79.99 more

You could give it to him in the form of some combination of magazines,
soda, cigarettes, gum, newspapers, motor oil, car deodorizers, candy
bars, washer fluid, anti-freeze, etc.  But he'd be there all day trying to
decide what he wants and making it all add up to exactly $79.99, and
there's a long line of other customers waiting behind him.

That's the beauty of cash money.  You can count out exactly the proper
amount, it only takes a few seconds and bada-bing, he's out of there and
back on the road.