There is only one way to find out – all you need is a giant pile of money and a vending machine that sells soda for $1.25: If you put in a dollar note and press the “return change” button, you will get the dollar note back directly. If you put in two dollar notes (the maximum it takes) at a time, it will give you change for the two dollars.
Our machine had $29 of change. It started out with 25¢ coins, and after a while returned a combination of different coins (25¢ & 10¢, then 10¢ & 5¢), finally switching to all 5¢ coins at the end.
In total, it had
- 25¢ x 57 = $14.25
- 10¢ x 114 = $11.40
- 5¢ x 67= $3.35
After this, the machine refused to take bills, so it was either full with bills or, more likely, out of change.
But actually, it might still contain up to 95¢ of change – today’s homework is to find out how to measure the remaining change in the machine!