# 5.4: Find the Percent of a Number

**At Grade**Created by: CK-12

**Practice**Percent of a Number

Do you like to ride roller coasters? Take a look at this dilemma.

At an amusement park there is an average of 30,000 visits daily. Over 75% of those people ride on the biggest roller coasters. About how many people ride the roller coasters?

**To figure this out, you will need to find the percent of a number. Pay attention and you will know how to solve this problem by the end of the Concept.**

### Guidance

We said that percent are very useful. Part of the usefulness is being able to find percentages of a number. In other words, if you are planning a barbecue and the butcher tells you that 30% of the people want chicken…well, how many people is that? For how many people should you buy chicken?

**The key words here are “of a number” this means that you multiply to solve the problem. We can convert the percent to a decimal and multiply or convert it to a fraction and multiply.**

Let’s suppose that you invited 58 people to the barbecue. If 30% prefer chicken, then we need to know how many people that is.

**First, convert 30% to either a decimal or a fraction**

\begin{align*}30\% = .30 \ or \ 30\% = \frac{30}{100} = \frac{3}{10}\end{align*}

**Using the decimal or fraction, you now multiply by the number of people you invited: \begin{align*}.30 \times 58 = 17.4\end{align*} or about 17 people**

Or

\begin{align*}\frac{3}{10} \times 58 = \frac{174}{10} = 17.4\end{align*} or about 17 people.

**This is the answer.**

Solve each problem.

#### Example A

What is 20% of 18?

**Solution: 3.6**

#### Example B

What is 25% of 40?

**Solution: 10**

#### Example C

What is 5% of 80?

**Solution: 4**

Now back to the dilemma from the beginning of the Concept.

First, let's write a statement about the problem.

We need to figure out 75% of 30,000.

To do this, first convert 75% to a decimal.

\begin{align*}75\% = .75\end{align*}

Next, multiply.

\begin{align*}.75 \times 30,000 = 22,500\end{align*}

**22,500 people ride the roller coasters.**

### Vocabulary

- Ratio
- a comparison between two quantities.

- Percent
- a ratio that is being compared to the quantity of 100. Percent means out of 100.

- Fraction
- a part of a whole written using a numerator and a denominator.

- Decimal
- a part of a whole written in base ten place value.

- Proportion
- two equal ratios form a proportion.

### Guided Practice

Here is one for you to try on your own.

A survey stated that 15% of the people surveyed like olives. Out of the 500 people surveyed, about how many like olives?

**Solution**

First, let's write a statement describing the problem.

15% of 500

Now change the percent to a decimal.

\begin{align*}15\% = .15\end{align*}

Next, multiply.

\begin{align*}.15 \times 500 = 75\end{align*}

**75 of the people like olives.**

### Video Review

### Practice

Find the percent of the given number by converting the percent to a decimal. You may round if necessary.

- 30% of 90
- 3% of 12
- 14% of 900
- 33% of 99
- 18% of 100
- 8% of 72
- 11% of 50
- 14.5% of 30
- 12% of 80
- 2% of 800
- 150% of 21
- 45% of 60

Read the following situations carefully and answer the questions accordingly.

- For every paycheck you receive, your employer pays 6% to social security. Write this percent as a ratio with a denominator of 100.
- Jimmy’s height is 1.78m. Write his height as a percent of a meter.
- A store did a survey and found that \begin{align*}\frac{4}{5}\end{align*} of its customers have shopped at its competitors’ stores within in the previous month. What percent is that?

Decimal

In common use, a decimal refers to part of a whole number. The numbers to the left of a decimal point represent whole numbers, and each number to the right of a decimal point represents a fractional part of a power of one-tenth. For instance: The decimal value 1.24 indicates 1 whole unit, 2 tenths, and 4 hundredths (commonly described as 24 hundredths).fraction

A fraction is a part of a whole. A fraction is written mathematically as one value on top of another, separated by a fraction bar. It is also called a*rational number*.

Percent

Percent means out of 100. It is a quantity written with a % sign.Proportion

A proportion is an equation that shows two equivalent ratios.### Image Attributions

Here you'll find the percent of a number using multiplication.