What Percent Means

Percent means per hundred: the sign % says 'out of 100'. If 25 of every 100 people in a town ride a bike, then 25% of the town rides. So $25\%$ is $\frac{25}{100}$, which is the decimal $0.25$: three ways to write the same number.

$100\%$ is 100 out of 100, the whole thing. 50% is half, 10% is a tenth, and 0% is none at all. A percent can also go past 100: 200% is twice the whole, the way a price can double.

Why use percents at all? Because they all compare to the same 100. Saying 18 out of 30 and 21 out of 35 makes you work to see which is bigger; as percents both are 60%, and you can see at once that they are equal.