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.
