AI Tutor
Next time you pass a gas station, look closely at the price sign — it doesn't say $3.45, it says $3.45⁹.
That tiny 9 means nine tenths of a single cent. Why do we track parts of a penny that we can't even hold in our hand?

Coins as Decimals

Money is a base-ten system where every step to the right is ten times smaller than the one before it.
A dime is worth 110\frac{1}{10} of a dollar ($0.10), and a penny is worth 1100\frac{1}{100} of a dollar ($0.01).
What happens if we take one single penny and slice it into ten equal pieces?

The Thousandths Place: The Mill

One tenth of a penny is called a mill, which equals one thousandth of a dollar ($0.001).
In 1792, the United States Congress officially defined the mill as 11,000\frac{1}{1,000} of a dollar to make precise tax and trade calculations.
Even though mills aren't minted as pocket coins today, companies still use them to set exact prices.
How do these tiny fractions add up to real money on a shopping receipt?