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3. Ratio and Rate
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Pre-Algebra /
Chapter 1
3. 

Ratio and Rate

This lesson delves into the mathematical concepts of ratio and rate, explaining how these are used in everyday life. For instance, it discusses how to calculate the unit rate to determine the best value when shopping for items like chocolate bars. It also explores how ratios can be used in cooking, such as determining the amount of ingredients needed for a homemade pizza. The concept of equivalent ratios is highlighted, which is useful for comparing different scenarios, like the cost per T-shirt or the speed of travel. Understanding these concepts is essential for making informed decisions in various aspects of life, including finance, cooking, and travel.
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Lesson Settings & Tools
10 Theory slides
10 Exercises - Grade E - A
Each lesson is meant to take 1-2 classroom sessions
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Ratio and Rate
Slide of 10
Consider some fun scenarios. Is there enough salsa for all these chips? What if the gas tank of the school bus has less gas than what it needs to make it to school? Amounts are compared to each other to find the right proportions. This lesson will explore similar situations where ratios and rates are used to create mixtures, calculate times, compare prices, and more.

Catch-Up and Review

Here is a recommended reading to go over before getting started with this lesson.

Explore

Mixing Colors to Create Shades of a Third Color

Play with the amount of each color to create shades of a third color.
Consider similar situations where two things are mixed to create a third one. How can situations like this be described?
Discussion

Ratio

A ratio is a comparison of two quantities that describes how much of one thing there is compared to another. Ratios are commonly represented using colon notation or as fractions. They are read as the ratio of to where is a non-zero number.

The ratio means that for every units of one quantity, there are units of another quantity. Ratios can be part-to-part or part-to-whole.

Part-To-Part Part-To-Whole
Explanation Describes how two different groups are related Describes the relationship between a specific group to a whole
Example The number of sophomores to freshmen on the basketball team is The number of sophomores to all basketball team members is
Example The number of mangoes to jackfruits the vendor has is The number of mangoes to all fruits the vendor has is
Ratios that express the same relationship between quantities are called equivalent ratios. For instance, consider the ratios of pages read per minute by Tearrik and by Zain.
These ratios can be simplified by finding the greatest common factor of their numerator and denominator. That factor can then be used to rewrite each ratio.
Fraction Form Greatest Common Factor Rewrite Simplify
Tearrik
Zain
These ratios are equivalent because both simplify to Equivalent ratios can be created by multiplying or dividing the numerator and denominator of a ratio by the same number.
Pop Quiz

Simplifying Ratios

The applet shows different ratios using colon notation. Write the simplest form of the indicated ratio. Consider that some ratios might already be in their simplest form.

An applet that generates random ratios. It asks for the simplest form of the given ratio.
Example

What Amount of Mushroom Is Needed for a Homemade Pizza?

It’s a beautiful Friday. Zain and their mother are celebrating their other parent's return home tonight after a week-long work trip. Zain's mother asks them for help to make homemade pizzas for dinner.

Pizza1.png

Their recipe is strict and claims that for every six olives on the pizza, two mushrooms must be added. If Zain plans to put olives on the pizza, how many mushrooms must the pizza have?

Hint

Write the ratio of the number of olives to the number of mushrooms. Write an equivalent ratio to the original ratio where the numerator of the new ratio is What number multiplied by gives Multiply by the number found previously to find the number of mushrooms needed.

Solution
The recipe claims that for every six olives on the pizza, two mushrooms must be added. At the moment, the number of olives to the number of mushrooms on the pizza is the following ratio.
Now, Zain and their mother have olives to put on the pizza. They want to know how many mushrooms they need to add to the pizza following the recipe exactly. This number can be found by writing an equivalent ratio to The new ratio will have a numerator of
Note that This means that must be multiplied by to find the missing number of the equivalent fraction.
In this equivalent ratio, represents the olives that Zain and their mother will put on the pizza. Additionally, represents the number of mushrooms corresponding to olives. What a delicious smell! The pizza is almost ready.
Example

Using Ratios to Mix Colors to Create a Desired Shade

The two pizzas Zain and their mother made are still in the oven, smelling amazing. They decide to pass time by planning another weekend project — paint their house the color of an orange poppy flower! They want it to be a specific shade of orange. This shade is a result of a mixture of red and yellow in a ratio of

Zain's mother says they will need a total of liters of this shade of orange. Then, they will need to calculate how many liters of yellow and red paint are necessary to create the mixture. Which option describes the right amount?

Hint

Find the total amount described by the given ratio. Use this total amount to write a part-to-whole ratio for each color. Write an equivalent ratio for one of the part-to-whole ratios. The denominator of this equivalent ratio is What number multiplied by gives Find the numerator of the equivalent ratio

Solution
Consider the ratio of red to yellow paint that creates the specific shade of orange the family chose.
This is a part-to-part ratio because it describes how much red paint there is in the mixture compared to the yellow paint. Note that the orange paint will consist of parts in total.
The amount of red paint compared to the total amount of paint in the mixture can be determined using this information. This means it is a part-to-whole ratio. This also allows for the calculation of the ratio for the yellow paint.
Part-To-Whole Ratios
Red Paint Yellow Paint
The amount of red and yellow paint needed for the liters of paint will be found using equivalent ratios. A ratio equivalent to the red paint ratio will be written. This equivalent ratio will have a denominator of
Both denominators are present. Check them and what is noticeable? Well, This means that the numerator of the equivalent ratio is given by calculating the product of and
This ratio can be expressed in words. Of the liters of paint, must be red to create the specific shade of orange Zain wants. The number of liters of yellow paint can be found by subtracting from
Zain's family needs liters of red paint and liters of yellow paint to create liters of the desired shade of orange. Their house is going to look so stylish!
Discussion

Rate

A rate is a ratio that compares two quantities measured in different units. For example, a certain species of bamboo grows feet in height in years. Then, is its rate of growth. Here are some other possible examples of rate.
Some example rates and the corresponding scenarios
Rates might be most useful when finding how much of something is per unit of something else. Such a comparison is called a unit rate. If the given rates are not already unit rates, they can be determined by some calculations. Dive deeper into two of the previous examples.
Scenario Rate Unit Rate
Kriz finds Pokémon every days. Pokémon per days,
Pokémon per days 		Pokémon per day,
Pokémon per year
At a party, candies were eaten by kids. candies per kids,
candies per kids 		candies per kid
Example

What if a Greater Amount of Pizzas Is Needed?

The two pizzas Zain and their mother prepared earlier were a such a great success. Now they are thinking to prepare more pizzas for a local charity.

Two pizzas placed together.
External credits: @macrovector
Recall that it took minutes to prepare two pizzas. How much time do they need to prepare pizzas if this rate is kept?

Hint

Write the rate for this situation. Divide the numerator and denominator of the rate by its denominator to find the unit rate. Multiply the unit rate by the number of pizzas that are needed. Divide the result by to get the number of hours of prep time.

Solution
This situation compares the time it takes to prepare the pizzas. Recall that it took Zain and their mother minutes to prepare pizzas. This rate can be written as a fraction.
Now, the numerator and denominator of this fraction will be divided by to find the unit rate.
This means that a pizza takes minutes to be ready. The time it will take to prepare pizzas can now be calculated by multiplying the unit rate by
Zain's family will spend about minutes to preparing the pizzas for the local charity. Notice that the answer is asked in hours. Divide by to get how many hours this time represents.
After hours, the pizzas are ready. Zain's family is taking them to the local charity. What a good lesson for Zain.
Example

Finding Missing Distances Using Rates

Zain realizes that their parent is so late arriving home. Zain calls. "Where are you?" The parent picks up and says, "Hey, Zain! I am miles away. I will be home in hours."

External credits: Hari Panicker
Zain's parent challenges them to find out how far this work trip was if it takes hours in total and the same rate is kept. How far was it?

Hint

Write the rate of the distance traveled to the time it takes as a fraction. Find the unit rate. Multiply the unit rate by hours.

Solution
Begin by writing the rate of the distance traveled to the time it takes as a fraction.
Now, divide the numerator and denominator of this rate by to find the unit rate of this situation.
The distance that Zain's parent traveled in hour is miles. Now, it is given that the total trip will take hours at this rate. Multiply the unit rate by to determine how far Zain's parent's work trip was.
Wow! Zain's parent's work trip was miles away. That is far, far away. Zain feels relieved to have figured out how soon their parent will be home.
Closure

Unit Rates Can Help to Identify the Best Deal

Think about going shopping at the market. There are tons of different brands, and the same brand usually offers the same product packaged in different sizes. Deciding what to buy can be overwhelming.

A really confused person.

People tend to think larger packages have a lower price per unit. Actually, that is true only sometimes. Comparing the unit rate will help decide whether buying more smaller packages or one large package offers a better deal. The unit rate describes the cost per pound, quart, kilogram, or other corresponding unit of measure.

Compare unit prices to find the best value for money.

Consider the following advertisement. Delicious standard-sized and giant-sized chocolate bars are on sale.

The prize and weight of the standard size chocolate bar and the giant size bar.

Is the giant-size bar a better option? Write the rates as fractions. That will help to find the unit rate for each bar later.

Standard-Size Giant-Size
Rate

Divide the numerator and denominator of the standard size rate by to get its unit rate. Similarly, divide the numerator and denominator of the giant size ratio by

Standard-Size Giant-Size
Rate
Unit Rate
Review the standard-size rate. The amount of chocolate when paying one dollar is ounces. On the other hand, the giant-size rate is ounces of chocolate per one dollar. This means buying smaller bars is better value for the buyer. The content of this lesson applies not only to chocolate, but to many real-life situations.



Level 1
Level 2
Level 3
Ratio and Rate
Exercises

Observe the given diagram and find the indicated ratio. Write the ratio in its fraction form.

What is the ratio of circles to triangles?

A diagram showing circles and triangles

What is the ratio of T-shirts to dresses?

A diagram showing T-shirts and dresses

What is the ratio of oranges to all fruits in the diagram?

A diagram showing oranges and other fruits

We want the ratio that compares the number of circles in the diagram to the number of triangles. In other words, we want a part-to-part ratio. Let's count the circles and triangles in the diagram.

We can see that there are 18 circles and 30 triangles. The number of circles represents the numerator of the ratio. The number of triangles gives its denominator. Let's write it! Ratio of◯ to △: 18/30 We can simplify this ratio using the greatest common factor GCF of 18 and 30. Let's write the factors of these numbers to find their GCF. &Factors of 18:1, 2, 3, 6, 9, 18 &Factors of 30:1, 2, 3, 5, 6, 10, 15, 30 The GCF( 18, 30)= 6. We can now rewrite the numerator and denominator of the ratio to simplify it. Ratio of◯ to △: 18/30=3*6/5*6 = 3/5 This means that for every three circles in the diagram, there are five triangles.

Let's now determine the ratio of T-shirts to dresses in the diagram. This is also a part-to-part ratio. Let's count each of them to find how many of each item there are.

There are 12 T-shirts and 5 dresses. The number of T-shirts represents the numerator of the ratio. The number of dresses gives the denominator of the ratio. Let's write it! Ratio of T-shirts to Dresses: 12/5

This part asks for the ratio of oranges to all fruits in the diagram. This represents a part-to-whole ratio. Let's first determine the number of oranges and the number of fruits that are not oranges.

We can see that there are 7 oranges. We also have 11 fruits that are not oranges. We will add these two numbers to find the total number of fruits in the diagram. Total Number of Fruits: 7+ 11= 18 Now, the number of oranges represents the numerator of the ratio. The total number of fruits is its denominator. The Ratio of Oranges to All Fruits: 7/18

The ratio of cups of flour to cups of milk for a pancake recipe is Identify the options that are equivalent to the given ratio.

Consider the ratio of cups of flour to cups of milk for the pancake recipe. 3:2 ⇔ 3/2 We will check each of the four ratios to see if any is equivalent to 3:2. Let's multiply or divide the numerator and the denominator of each of these ratios by the same number to see if it produces the ratio 3:2. Let's begin with the ratio 9:6. 9:6 ⇔ 9÷ 3/6÷ 3=3/2 We can see that dividing the numerator and the denominator of the ratio 9:6 by 3 results in the ratio 3:2. This means that this ratio is equivalent to the ratio 3:2. Now, let's check the ratio 8:7. 8:7 ⇔ 8/7 The denominator of this fraction is 7, which is a prime number. This number cannot be divided anymore. This means that this fraction cannot be simplified and cannot be equal to 3:2. Now, let's check the ratio 4:3. 4:3 ⇔ 4/3 This ratio has a similar situation to the previous one. Its denominator is a prime number. This ratio is also in its simplest form. This means that the ratio 4:3 is not equivalent to the ratio 3:2. Finally, let's look at the ratio 6:4. 6:4 ⇔ 6÷ 2/4÷ 2=3/2 The ratio 6:4 is equivalent to the ratio 3:2. Let's summarize our results in a table.

Ratio Equivalent to 3:2?
9:6 Yes
8:7 No
4:3 No
6:4 Yes
A clothes store sells T-shirts for What is the cost per T-shirt?
Dylan bikes miles in hours. How many miles per hour does he travel?

This situation compares dollars to T-shirts because it asks for the cost of a T-shirt. We can begin by writing this rate as a fraction. $16/4T-shirts We can now use this rate to find its unit rate. That will give us the cost of a T-shirt. Let's divide the numerator and the denominator of this rate by its denominator to get the unit rate.

Rate Unit Rate
$16/4T-shirts 16÷ 4/4 ÷ 4=$4/1T-shirt

This means that the cost per T-shirt is $4.

We want now to find how many miles Dylan travels. Let's first write the rate of distance traveled to the time it takes as a fraction. 48Miles/6 Hours We can now find the unit rate by following a similar process as in the previous part. Let's divide the numerator and the denominator of this rate by 6.

Rate Unit Rate
48Miles/6 Hours 48÷ 6/6 ÷ 6=8Miles/1Hour

This means that Dylan travels 8 miles per hour.

Read each situation carefully. Identify which is different from the others.

Let's look at the given situations.

These situations represent rates because they compare two different measures, kilograms and meters. Let's write the rate for each to find its unit rate. This way, we can compare them and see which one is different. Let's look at the first one. 9kg : 3m Now, we can divide both units by 3 to get the unit rate. 9/3kg : 3/3m [0.3em] ⇕ [0.3em] 3kg: 1m We can continue the same way to find the rest of the ratios.

Situation Rate Divide Unit Rate
9 kilograms for every 3 meters 9kg : 3m 9/3kg : 3/3m 3kg:1m
12 kilograms per 3 meters 12kg : 3m 12/3kg : 3/3m 4kg:1m
18 kilograms for every 6 meters 18kg : 6m 18/6kg : 6/6m 3kg:1m
15 kilograms per 5 meters 15kg : 5m 15/5kg : 5/5m 3kg:1m

Note that three out of four rates have the same unit rate of 3 kilograms per meter. This means that they are equivalent ratios. The only rate that does not belong with the other three is 12 kilograms per 3 meters because it has a unit rate of 4 kilograms per meter.

Ratio and Rate

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