Mathematics Grade 9 15 min

Solve proportions word problems

Solve proportions word problems

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Introduction & Learning Objectives

Learning Objectives Identify proportional relationships described in word problems. Translate a word problem into a mathematical proportion with an unknown variable. Set up proportions with consistent units in the numerators and denominators. Solve for the unknown variable in a proportion using the cross-multiplication method. Interpret the solution in the context of the original problem. Verify that their answer is reasonable for the given scenario. Ever wonder how a tiny map can guide you through a huge city or how to adjust a recipe for more people? 🗺️ Proportions are the secret! This tutorial will teach you how to set up and solve proportion word problems, a powerful skill for making accurate comparisons and predictions. You'll learn a step-by-step method to turn r...
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Key Concepts & Vocabulary

TermDefinitionExample RatioA comparison of two quantities by division, often expressed as a fraction (a/b), with a colon (a:b), or using the word 'to' (a to b).In a class with 15 boys and 10 girls, the ratio of boys to girls is 15/10, which simplifies to 3/2. RateA special type of ratio that compares two quantities with different units.A car travels 180 kilometers in 3 hours. The rate is 180 km / 3 hours. Unit RateA rate where the second quantity (the denominator) is one unit.If a car travels 180 km in 3 hours, its unit rate is 60 km/hour (60 kilometers per 1 hour). ProportionAn equation stating that two ratios or rates are equivalent.The ratio 2/4 is proportional to 3/6 because they both simplify to 1/2. The proportion is written as 2/4 = 3/6. Cross-ProductsIn a proportion, the...
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Core Formulas

Setting Up a Proportion \frac{a}{b} = \frac{c}{d} To set up a proportion from a word problem, create two equivalent ratios. Ensure the units are consistent across the numerators and across the denominators. For example, (kilometers/hours) = (kilometers/hours). Cross-Multiplication Property If \frac{a}{b} = \frac{c}{d}, then a \cdot d = b \cdot c This is the primary method for solving proportions. Multiply the numerator of the first fraction by the denominator of the second, and set it equal to the product of the denominator of the first fraction and the numerator of the second. Then, solve the resulting algebraic equation for the variable.

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Sample Practice Questions

Challenging
The ratio of the side lengths of a rectangle is 5:2. If the perimeter of the rectangle is 84 cm, what is its area?
A.120 cm²
B.360 cm²
C.400 cm²
D.840 cm²
Challenging
In a direct proportion, the ratio of x to y is constant. If the ratio of (x+3) to 4 is the same as the ratio of 10 to (x-3), what is a possible value of x?
A.5
B.3
C.4
D.8
Challenging
A factory has two machines, A and B, that produce widgets at a constant rate. Machine A produces 200 widgets in 50 minutes. Machine B produces 300 widgets in 60 minutes. If both machines run simultaneously, how many minutes will it take them to produce a combined total of 1,800 widgets?
A.150 minutes
B.225 minutes
C.450 minutes
D.200 minutes

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