7.1 - Recalling Ratios and Percentages
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Understanding Ratios
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today we're learning about ratios! Can anyone tell me what a ratio means?
Is it like comparing two numbers?
Exactly! A ratio compares two quantities. For instance, if we have 20 apples and 5 oranges, we can say the ratio of oranges to apples is 5:20, which simplifies to 1:4. Who can express this as a fraction?
That would be \frac{5}{20} = \frac{1}{4}!
Great job! Remember, this means for every 4 apples, there is 1 orange.
Converting Ratios to Percentages
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now, let's connect ratios to percentages. If I have 5 oranges in a basket of 25 fruits, how do we find the percentage of oranges?
We can take 5 divided by 25 and multiply it by 100!
That's correct! So, we have: \( \frac{5}{25} \times 100 = 20\% \). What about apples?
The apples would be 100% - 20%, which is 80%!
Right! Always remember that the total percentage must add up to 100.
Applying Ratios and Percentages in Practical Situations
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Imagine we're planning a picnic, and 60% of the total students are girls. If there are 18 girls, how do we figure out the total number of students?
We can set up an equation! If 60% of students are 18, then \( x = \frac{18 \times 100}{60} = 30 \).
Exactly! Now, how many boys are there?
30 total students minus 18 girls means there are 12 boys.
Great work! The ratio of girls to boys is 18:12 or simplified to 3:2.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, students learn how to express the relationship between two quantities using ratios and percentages. Examples highlight the practical application of these concepts in real-life scenarios, emphasizing how to convert between ratios and percentages and solve related problems.
Detailed
Recapping Ratios and Percentages
In Section 7.1, we explore the fundamental concepts of ratios and percentages as tools for comparing quantities. A ratio is defined as a relationship between two numbers that indicates how many times the first number contains the second. For example, if you have 20 apples and 5 oranges, the ratios of oranges to apples is given as 5:20, which can be simplified to 1:4. This relationship can also be represented as a fraction:
$$\frac{5}{20} = \frac{1}{4}$$
Conversions from ratios to percentages help to visualize relationships better. For instance, in a basket containing only apples and oranges, if 5 out of 25 fruits are oranges, then:
$$\text{Percentage of oranges} = \frac{5}{25} \times 100 = 20\%$$
Conversely, the percentage of apples will be 100% - 20% = 80%. The concept is practical, illustrated with examples including calculating the ratio of girls to boys in a class and determining transport costs for an upcoming school picnic. Exercises reinforce these ideas, inviting students to convert ratios to percentages and explore various contextual problems. By understanding these concepts, students gain essential skills for mathematical and everyday problem solving.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Understanding Ratios
Chapter 1 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
We know, ratio means comparing two quantities. A basket has two types of fruits, say, 20 apples and 5 oranges. Then, the ratio of the number of oranges to the number of apples = 5 : 20.
Detailed Explanation
A ratio is a way to compare two quantities. In this case, we compare the number of oranges to the number of apples. With 5 oranges and 20 apples, we say the ratio is 5:20, which simplifies to 1:4. This means that for every 1 orange, there are 4 apples.
Examples & Analogies
Think of a recipe that calls for 1 cup of sugar and 4 cups of flour. The ratio of sugar to flour is 1:4. If you double the recipe, you'll have 2 cups of sugar and 8 cups of flour, but the ratio remains the same.
Using Fractions with Ratios
Chapter 2 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
The comparison can be done by using fractions as, 5/20 = 1/4. The number of oranges is 1/4 of the number of apples. In terms of ratio, this is 1 : 4, read as, “1 is to 4”.
Detailed Explanation
Ratios can also be expressed as fractions. Here, we see that there are 5 oranges out of 20 total fruits, which can be simplified to the fraction 1/4. This fraction tells us that the number of oranges is one fourth of the number of apples.
Examples & Analogies
If a class has 10 boys and 40 girls, the ratio of boys to girls is 10:40, which simplifies to 1:4. This tells you that for every boy, there are four girls in the class.
Ratios Versus Percentages
Chapter 3 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
This comparison can also be done using percentages. There are 5 oranges out of 25 fruits. By unitary method: So percentage of oranges is (5/25) x 100 = 20%.
Detailed Explanation
Percentages provide another way to compare quantities. Here, if there are 5 oranges out of a total of 25 fruits, we can calculate the percentage of oranges by dividing the number of oranges by the total number of fruits and multiplying by 100. This gives us 20%, meaning 20% of the fruits in the basket are oranges.
Examples & Analogies
Imagine you have a box of 100 chocolates. If 20 chocolates are dark chocolate, then the percentage of dark chocolates is (20/100) x 100 = 20%. This helps you understand what fraction of the total is made up of dark chocolates.
Total Percentages in a Group
Chapter 4 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Since the basket contains only apples and oranges, So, percentage of apples + percentage of oranges = 100 or percentage of apples + 20% = 100 or percentage of apples = 100 – 20 = 80.
Detailed Explanation
In a situation where you have only two types of items, the total of their percentages must equal 100%. So if the percentage of oranges is 20%, the percentage of apples must be 100% - 20% = 80%. This is useful for understanding how two parts make up a whole.
Examples & Analogies
If you and your friend have a collection of 50 stickers where you have 30 and your friend has 20, you can easily see that your share, 30 stickers, is 60% (30/50 * 100) of the total collection.
Application Example of Ratios in a Picnic Planning
Chapter 5 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
Example: A picnic is being planned in a school for Class VII. Girls are 60% of the total number of students and are 18 in number.
Detailed Explanation
In this example, 60% of the total students are girls. When we know that there are 18 girls, we can use this information to find out how many total students there are. If 60% represents 18 girls, we can determine the total number by setting up the equation where 60% of the total number equals 18.
Examples & Analogies
If in a class of 30 students, 60% are girls, we can calculate that there are 18 girls. Conversely, if we see 18 girls, knowing they comprise 60% of the class allows us to find out that the total class size is 30.
Finding Costs and Distances
Chapter 6 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
The picnic site is 55 km from the school and the transport company is charging at the rate of ₹12 per km.
Detailed Explanation
To find out the total cost of transport for the picnic, we multiply the distance to the picnic site (55 km) by the rate charged by the company (₹12 per km). This kind of calculation helps budget for events like school picnics realistically.
Examples & Analogies
If a taxi service charges ₹10 per kilometer and you need to travel 10 km, your total fare will be ₹10 x 10 = ₹100. Planning a school field trip follows similar budgeting where distances and costs are calculated to ensure everything fits within the budget.
Understanding Budget Distribution in a Picnic
Chapter 7 of 7
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
The total cost of refreshments will be ₹4280. Can you tell the ratio of girls to boys in the class?
Detailed Explanation
In planning events like picnics, knowing the total budget and how many students are involved helps understand and manage costs for food and activities. Here, we would compare the number of girls to the boys once we determine how many boys are there using the total student count derived from the earlier percentage calculations.
Examples & Analogies
If you are throwing a birthday party and have a total budget of ₹5000, and you know food costs ₹2500, you can easily determine how much money you have left to spend on games and decorations.
Key Concepts
-
Ratio: The comparison of two quantities expressed in a fraction or standard form.
-
Percentage: A way to express a number as a fraction of 100.
-
Unitary Method: A method used to find one unit's value to derive other related values.
Examples & Applications
Example of ratio: In a basket of 20 apples and 5 oranges, the ratio of oranges to apples is 5:20.
Example of percentage: If there are 5 oranges out of 25 fruits, the percentage of oranges is \( \frac{5}{25} \times 100 = 20\%. \)
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
To find the percentage, take part of the whole, then multiply by 100 – that’s your goal!
Stories
Imagine a fruit basket filled with fruits. Counting apples and oranges teaches us how to compare using ratios and percentages.
Memory Tools
For Ratios: Remember R for Relation and P for Percentage, you calculate based on total counts.
Acronyms
RAP
Ratios And Percentages
remember to RAP your calculations with care!
Flash Cards
Glossary
- Ratio
A comparison of two quantities indicating how many times one value contains the other.
- Percentage
A proportion or fraction out of 100, representing a part of a whole.
- Quantity
An amount or number of a particular item or substance.
- Unitary Method
A technique used to find the value of one unit based on the known value of multiple units.
Reference links
Supplementary resources to enhance your learning experience.