Lesson 1: What is a Percent?

Property

"Percent" means "for each 100" or "out of 100." So a percent is just a fraction whose denominator is 100. For example, $75\% = 0.75 = \frac{75}{100}$. Because 10% is equal to $\frac{1}{10}$, it is easy to find 10% of a number: we just divide the number by 10.

Examples

• A store offers a 10% discount on a 90 dollar jacket. The discount is $\frac{1}{10}$ of 90 dollars, which is $90 \div 10 = 9$ dollars.
• To find 20% of 500, first find 10% by dividing by 10, which is $500 \div 10 = 50$. Then, double it for 20%, so $2 \times 50 = 100$.
• A restaurant bill is 40 dollars. A 15% tip can be found by taking 10% (4 dollars) and adding 5% (half of 10%, which is 2 dollars). The total tip is $4 + 2 = 6$ dollars.

Explanation

Think of the percent sign (%) as shorthand for "out of 100." It's a simple way to discuss parts of a whole. Knowing shortcuts, like 10% being one-tenth of a number, makes mental math much faster and easier.

Property

$100\% = 1$ (the complete whole)
This means that 100% represents the entire quantity or the complete amount of something.

Examples