Grade 7 → Ratio and Proportion → Ratios ↓
Understanding Ratios
In math, a ratio is a way of comparing two quantities. It tells us how much of one thing is compared to another. Ratios can be used to describe relationships between numbers, quantities, sizes, and almost anything that can be counted or measured. Understanding ratios is important because they are used in everyday life, from cooking recipes to scaling models, determining speed, and more.
What is the ratio?
Ratio is a comparison between two or more numbers. It tells us how many times one number contains another number. For example, if a basket contains 2 apples and 3 oranges, then the ratio of apples and oranges is 2:3.
Expressing ratios
Ratios can be expressed in three different ways:
- Use of the colon (:) symbol, such as
2:3
- In fractional form, such as
2/3
- Use of the word "to", such as
2 to 3
Visual example of proportions
To understand proportions better, let's look at a visual illustration:
In the above visualization, we have 1 blue rectangle and 2 green rectangles. The ratio of the blue and green rectangles is:
1:2
Simple text examples of ratios
Consider the following examples:
4:5
.3:2
.Understanding and solving ratio problems
To solve problems involving ratios, you may need to find unknown quantities. Let's learn how to do this through some methods and examples.
Finding unknowns from proportional ratios
Sometimes, you need to find an unknown number in a given ratio. Here's a basic example to make it clear:
3:4
and there are 12 boys, then how many girls are there?Solution:
Let the number of girls be
x
. We determine the ratio as follows3/4 = 12/x
To solve for x
, cross-multiply: 3 * x = 4 * 12
Simplification:
3x = 48
x = 48 / 3
x = 16
So, there are 16 girls in the class.
Scaling with proportions
Ratios are often used to increase or decrease scale. This is useful in models, maps, and more. If a map has a scale ratio of 1:1000, it means that 1 unit on the map is equal to 1000 units in real life.
Importance of ratios in real life
Ratios are not just mathematical concepts; they are extremely useful in real-world scenarios. Below are some areas where ratios play an important role:
- Cooking: Proportions are often used in recipes to ensure the correct balance of ingredients.
- Business: Businesses use ratios to measure performance, such as profit margins and debt-to-equity ratios.
- Construction: When measuring a model of a building or designing blueprints.
- Science: Ratios are used to mix chemicals in a proportionate manner.
- Maps and Navigation: Ratios are used to indicate scale on maps.
Equivalent ratio
Just like fractions, ratios can also have equivalent forms. For example, the ratio of 2:3
is equivalent to 4:6
, 6:9
etc. These ratios can be simplified or expanded according to the problem.
Given ratio:
2:3
Multiply each part of the ratio by the same number, say
2
:(2 * 2):(3 * 2) = 4:6
(2 * 3):(3 * 3) = 6:9
All of these are equal to
2:3
.Converting ratios to fractions
You can convert any ratio into a fraction to solve problems or perform calculations. For example, a ratio of 4:5
can be written as a fraction:
4/5
This fraction can be used with other fractions or converted to a decimal if needed.
Ratio as a tool for comparison
Ratios provide a clear way to compare quantities. For example, if car A can travel 30 miles on 1 gallon of fuel and car B can travel 40 miles on the same quantity, the ratio of their efficiencies is 30:40
which simply becomes 3:4
.
Practice problems
Let's look at some practice problems to help you try to understand ratios:
Solution:
Total number of balls =
8 + 12 = 20
Ratio of total red balls =
8:20
, which simplifies to 2:5
.5:6
and there are 120 boys, then how many girls are there?Solution:
Let the number of girls be
y
.5/6 = y/120
Cross-multiply: 5 * 120 = 6 * y
Simplification:
600 = 6y
y = 600 / 6
y = 100
So, there are 100 girls here.
Proportion in proportion
When two ratios are equal, they are said to be in proportion. For example, if the length and width of one rectangle are in the ratio of 4:5
and the length and width of another rectangle are in the ratio of 8:10
, then these rectangles are in proportion because:
4/5 = 8/10
Conclusion
Ratios are a fundamental part of mathematics that helps describe the relationships between quantities. By mastering ratios, you can better understand and solve real-world problems, improve numeric literacy, and enhance important mathematical skills. Whether you're cooking, studying, or working on complex engineering problems, ratios are an important tool that can help us understand the world around us.