Mathematics
Grade 7
15 min
Equivalent ratios
Equivalent ratios
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1
Introduction & Learning Objectives
Learning Objectives
Define what an equivalent ratio is.
Identify if two given ratios are equivalent.
Generate equivalent ratios by multiplying both terms by the same non-zero number.
Generate equivalent ratios by dividing both terms by the same non-zero number.
Express a ratio in its simplest form.
Solve real-world problems involving equivalent ratios.
Have you ever followed a recipe and needed to double it? 🍳 Or perhaps you've seen different sized maps, but they all show the same places? These situations often involve equivalent ratios!
In this lesson, you'll discover what equivalent ratios are and how they represent the same relationship between quantities, even if the numbers look different. Understanding equivalent ratios is crucial for scaling recipes, compa...
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Key Concepts & Vocabulary
TermDefinitionExample
RatioA comparison of two quantities by division. It can be written as a:b, a/b, or 'a to b'.If there are 3 apples and 2 bananas, the ratio of apples to bananas is 3:2.
Equivalent RatiosRatios that express the same relationship between two quantities, even though the numbers themselves might be different. They simplify to the same basic ratio.The ratios 1:2 and 2:4 are equivalent because they both represent the same proportional relationship.
Simplest Form (of a Ratio)A ratio is in its simplest form when the two quantities (terms) have no common factors other than 1. It's like simplifying a fraction.The ratio 6:9 in simplest form is 2:3, because both 6 and 9 can be divided by their greatest common factor, 3.
Scaling Up RatiosCreating an equivalent ratio...
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Core Formulas
Generating Equivalent Ratios (Multiplication)
If $a:b$ is a ratio, then $a \times c : b \times c$ is an equivalent ratio, where $c$ is any non-zero number.
To find an equivalent ratio with larger numbers, multiply both parts of the ratio by the same non-zero number. This is called 'scaling up'.
Generating Equivalent Ratios (Division)
If $a:b$ is a ratio, then $a \div c : b \div c$ is an equivalent ratio, where $c$ is any common non-zero factor of $a$ and $b$.
To find an equivalent ratio with smaller numbers or to simplify a ratio, divide both parts of the ratio by the same common non-zero factor. This is called 'scaling down'.
Checking for Equivalence (Cross-Multiplication)
Two ratios $a:b$ and $c:d$ are equivalent if and only if $a \times d = b \ti...
5 more steps in this tutorial
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Challenging
The ratio of two numbers is 5:8. If their sum is 117, what is the value of the larger number?
A.45
B.65
C.72
D.9
Challenging
A student is told that 6:10 and 9:15 are equivalent. They notice that 6+3=9 and 10+5=15. They conclude that you can create equivalent ratios by adding different numbers. Why is their reasoning flawed?
A.Their addition is incorrect; 10+5 is not 15.
B.The ratios 6:10 and 9:15 are not actually equivalent.
C.The rule is that you must add the same number to both terms, not different numbers.
D.It is a coincidence; the rule for equivalence is multiplicative, not additive, and this example doesn't prove a general rule.
Challenging
The ratio of the length to the width of a rectangle is 7:3. If the perimeter of the rectangle is 120 cm, what is its area?
A.864 cm²
B.756 cm²
C.2100 cm²
D.1200 cm²
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