3. Turning Data into Percents

A percent is a part out of 100. To find what percent one number is of another:
\[ \text{percent} = \frac{\text{part}}{\text{whole}} \times 100. \]

Worked example: 18 of 24 students passed a quiz. What percent passed?
\[ \frac{18}{24} \times 100 = 0.75 \times 100 = 75\%. \]

Worked example (percent of a total): a survey of 200 people found 30% prefer tea. How many people is that?
\[ 0.30 \times 200 = 60 \text{ people.} \]

Percent change tells you how much something grew or shrank:
\[ \text{percent change} = \frac{\text{new} - \text{old}}{\text{old}} \times 100. \]
If a price rises from $50 to $60: \(\frac{60 - 50}{50} \times 100 = 20\%\) increase.