Mathematics
Grade 9
15 min
Solve proportions
Solve proportions
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1
Introduction & Learning Objectives
Learning Objectives
Define a proportion and identify its parts (means and extremes).
Set up a proportion correctly from a given word problem or scenario.
Solve for an unknown variable in a proportion using the cross-product property.
Solve proportions that include binomial expressions, requiring use of the distributive property.
Apply proportional reasoning to solve real-world problems involving scaling, similar figures, and rates.
Verify the solution of a proportion by substitution.
Ever wonder how architects create tiny scale models of giant skyscrapers? They use the power of proportions to make sure every part is perfectly scaled! 🏙️
This tutorial will guide you through the process of solving proportions. You will learn how to set up and solve these powerful equations, w...
2
Key Concepts & Vocabulary
TermDefinitionExample
RatioA comparison of two quantities by division. It can be written in three ways: a to b, a:b, or as a fraction a/b.The ratio of 3 apples to 5 oranges is 3:5 or 3/5.
ProportionAn equation that states that two ratios are equivalent.The equation \frac{1}{2} = \frac{4}{8} is a proportion because both ratios represent the same value.
Cross-ProductsIn a proportion \frac{a}{b} = \frac{c}{d}, the cross-products are the product of the numerator of the first ratio and the denominator of the second (a*d), and the product of the denominator of the first ratio and the numerator of the second (b*c).In the proportion \frac{2}{3} = \frac{4}{6}, the cross-products are 2 * 6 and 3 * 4. Both equal 12.
ExtremesIn a proportion written as a:b = c:d, the extremes are the first and last te...
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Core Formulas
The Proportion Equation
\frac{a}{b} = \frac{c}{d}
This is the fundamental structure of a proportion, where two ratios are set equal to each other. The values b and d cannot be zero.
The Cross-Product Property
If \frac{a}{b} = \frac{c}{d}, then a \cdot d = b \cdot c
This property is the primary method for solving proportions. It states that the product of the means equals the product of the extremes. This converts the proportion into a linear equation that can be solved for an unknown variable.
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Challenging
Solve for x, given x > 0: \frac{x}{2} = \frac{8}{x}
A.16
B.8
C.4
D.2
Challenging
A high-speed printer can print 400 pages in 5 minutes. How many hours will it take to print a 4,800-page report?
A.0.5 hours
B.1 hour
C.1.5 hours
D.2 hours
Challenging
In the proportion \frac{a}{b} = \frac{c}{x}, which of the following correctly expresses x in terms of a, b, and c?
A.x = \frac{ac}{b}
B.x = \frac{ab}{c}
C.x = \frac{bc}{a}
D.x = abc
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