In this section, you will learn about ratios and proportions, the proportion definition in math, as well as the types of proportions with proportion examples.
Check-out the interactive simulations to know more about the lesson and try your hand at solving a few interesting practice questions at the end of the page.
Now that you know what you're going to learn, maybe it's time to give you an introduction. But where is a proper introduction without an example?
Let's say, you and your friend went to a store to purchase some notebooks. The ratio of purchase is \(3:10\) and the ration of cost is \(15: 50\). Whose notebooks were costlier?
Well, in order to answer that, let's check out both ratios.
First, let's point out that both ratio values are equal i.e. if you simplify \(15:50\), you get \(3:10\)
This means, you and your friend paid the same amount for the notebooks.
These ratios are in proportion and can be written as
\(3:10::15:50\)
Lesson Plan
What is a Proportion?
Proportion - Definition
Proportion definition says that when two ratios are equivalent, they are in proportion.
Proportion is a mathematical comparison between two numbers.
Ratios and Proportions
Ratio is a way of comparing two quantities of the same kind by using division.
The ratio formula is used to compare the relationship between two numbers of the same kind.
The ratio formula for two numbers \(a\) and \(b\) is given by \(\begin{align}a:b \end{align}\) or \(\begin{align} \frac{a}{b} \end{align}\)
- \(\frac{a}{b} = \frac{c}{d} \implies \frac{b}{a}=\frac{d}{c}\)
- \(\frac{a}{b} = \frac{c}{d} \implies \frac{a}{c}=\frac{b}{d}\)
- \(\frac{a}{b} = \frac{c}{d} \implies \frac{a+b}{b}=\frac{c+d}{d}\)
- \(\frac{a}{b} = \frac{c}{d} \implies \frac{a-b}{b}=\frac{c-d}{d}\)
- \(\frac{a}{b} = \frac{c}{d} \implies \frac{a+b}{a-b}=\frac{c+d}{c-d}\)
- If both the numbers \(a\) and \(b\) are multiplied or divided by the same number in the ratio \(a:b\), then the resulting ratio remains the same as the original ratio
Proportion Formula with Examples
Proportion Formula
We write it as \(a : b : : c : d\) or \(a : b = c : d\)
We read it as “\(a\) is to \(b\) as \(c\) is to \(d\).”
A proportion formula is an equation that can be solved to get the comparison values.
To solve proportion problems, we use the concept that proportion is two ratios that are equal to each other.
We mean this in the sense of two fractions being equal to each other.
For instance,
\[\begin{align}5 : 10 = \frac{5}{10} = \frac{1}{2} = 1 : 2\end{align}\]
Solved Examples
Let's explore some proportions examples below:
| Example 1 |
My mother's recipe to make pancakes says, "You have to use 2 eggs to make 20 pancakes."
How many eggs will I need to make 100 pancakes?
| Eggs | Pancakes | |
|---|---|---|
| Small amount | 2 | 20 |
| Large amount | \(x\) | 100 |
Solution
We know that \(\text{eggs} \propto \text{pancakes}\)
If we write the unknown number in the numerator, then we can solve this as any other equation.
\[\begin{align}\frac{x}{100}=\frac{2}{20}\end{align}\]
Multiplying 100 on both sides
\[\begin{align}100\times\frac{x}{100}&=100\times\frac{2}{20}\\x&=\frac{200}{20}\\&=10\end{align}\]
| \(\therefore\) We need 10 eggs to make 100 pancakes |
| Example 2 |
Jessy runs 4 miles in 30 minutes.
At this rate, how far could she run in 45 minutes?
Solution
Let's assume the unknown quantity here is \(x\)
In this case, \(x\) is the number of miles Jessy can run in 45 minutes at the given rate.
It is given that running 4 miles in 30 minutes is the same as running \(x\) miles in 45 minutes.
\[\begin{align}\frac{4}{30} &= \frac{x}{45}\\30 \times x &= 4\times 45\\x&=180\div 30\\ &= 6\end{align}\]
| \(\therefore\) Jessy can run 6 miles in 45 minutes |
| Example 3 |
In an apartment, nine taps can fill a full tank in four hours.
How long do you think it will take if twelve taps of same flow-rate are used to fill the same tank?
Does it fill the tank faster or does it slow the process?
Solution
This is inverse proportion problem.
Therefore, as the number of taps increases, inversely the time taken to fill the tank decreases.
Let us assume that the time taken to fill the same tank using 12 taps is \(x\) hours.
\[\begin{align}\frac{9}{x} &= \frac{12}{4}\\ 12x &= 9 \times 4 \\ x &= 36 \div 12 \\ x&=3 \end{align}\]
| \(\therefore\) 12 taps will take 3 hours and fill the tank faster |
| Example 4 |
If \(\Delta ABC\) has a perimeter of 12 units and is similar to \(\Delta RST\) with a scale factor of \(\begin{align}\frac{1}{3}\end{align}\)
Can you find the perimeter of \(\Delta RST\)?
Solution
Let \(x\) represent the perimeter of \(\Delta RST\)
Scale factor implies that the perimeters are in proportion to this ratio.
The proportion will be as follows.
\[\begin{align} \frac{1}{3} &= \frac{12}{x}\\x&= 3\times12 \\ &=36\end{align}\]
| \(\therefore\) The perimeter of \(\Delta RST\) is 36 units |
| Example 5 |
I want to make a nice fluffy cake on my mother's birthday.
To bake a perfect cake, I need to use sugar and flour in the proportion of 1:1
If I have 3 ounces of sugar available to make a 6 ounces cake, how many kilograms of flour is required?
The simulation below will show you the right mixing proportions for the cake.
Solution
Let the quantity of flour required be \(x\) ounces.
We know that 3 ounces of sugar is required for a 6 ounces of cake.
We need to find the quantity of flour required for a 6 ounces cake.
The proportion will be
\[\begin{align} \frac{1}{1} &= \frac{x}{3}\\ x&=3\end{align}\]
| \(\therefore\) 3 ounces of flour is needed |
Types of Proportions
There are two types of proportions.
- Direct Proportion
- Indirect Proportion
Direct Proportion
This type describes the direct relationship between two quantities.
In simple words, if one quantity increases, the other quantity also increases and vice-versa.
For example, if the speed of a car is increased, it covers more distance in a fixed amount of time.
In notation, direct proportion is written as
| \(y\propto x\) |
Inverse Proportion
This type describes the indirect relationship between two quantities.
In simple words, if one quantity increases, the other quantity decreases and vice-versa.
For example, increasing the speed of the car will result in covering a fixed distance in less time.
In notation, inverse proportion is written as
| \(y\propto\frac{1}{x}\) |
- Proportion is a mathematical comparison between two numbers.
- Basic proportions are of two types : Direct Proportions and Indirect Proportions.
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We can apply the concepts of proportions to geography, comparing quantities in physics, dietetics, cooking, etc.
Interactive Questions
Here are few activities for you to practice. Select/type your answer and click the "Check Answer" button to see the result.
Let's Summarize
We hope you enjoyed learning about Proportion with the simulations and practice questions. Now you will be able to easily solve problems on ratios and proportions, types of proportion, proportion-math examples.
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Important Topics
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Frequently Asked Questions (FAQs)
1. What are some ratio and proportion examples?
Grocery shopping is a good example of ratio and proportion in daily life.
You go to a grocery store and the shopkeeper gives you two options:
- 10 ounces packet of cereal costs $200
- 20 ounces packet of cereal costs $300
Here, comparing by division helps rather than comparing by finding the difference to find the best buy.
2. How do you know if two ratios form a proportion?
If two ratios are equivalent to each other, then they are proportional.
Here, the ratios 1:3, 2:6, and 3:9 are equivalent ratios.
3. How do you calculate proportion?
Proportion is calculated using the proportion formula which says
a : b : : c : d or a : b = c : d
We read it as “a" is to "b" as "c" is to "d”.