Mathematics
Grade 9
15 min
Unit rates
Unit rates
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Introduction & Learning Objectives
Learning Objectives
Define the terms ratio, rate, and unit rate, and differentiate between them.
Calculate a unit rate from a given rate with different units.
Use unit rates to compare values and determine the 'better buy' in real-world scenarios.
Solve multi-step problems involving speed, density, and other common unit rates.
Convert rates from one set of units to another using dimensional analysis (e.g., km/h to m/s).
Interpret the unit rate as the constant of proportionality (slope) in a linear relationship.
You're at the store and see two different sizes of your favorite snack. Which one is the better deal? 🛒 Unit rates are the mathematical tool you need to become a savvy shopper!
This tutorial will explore the concept of unit rates, which are a powerful...
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Key Concepts & Vocabulary
TermDefinitionExample
RatioA comparison of two or more quantities, often expressed with a colon or as a fraction. The quantities being compared may or may not have the same units.The ratio of teachers to students in a school is 1:25 or 1/25.
RateA special type of ratio that compares two quantities measured in different units.A car travels 240 kilometers in 3 hours. The rate is 240 km / 3 hours.
Unit RateA rate that has been simplified so that the second quantity (the denominator) is 1.The car's rate of 240 km in 3 hours simplifies to a unit rate of 80 km per 1 hour (or 80 km/h).
ProportionAn equation stating that two ratios or rates are equivalent. Proportions are often used to solve for an unknown quantity.240 km / 3 hours = x km / 1 hour. Solving for x gives the unit rate.
Dimensio...
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Core Formulas
Calculating a Unit Rate
\text{Unit Rate} = \frac{\text{Quantity A}}{\text{Quantity B}}
To find the rate 'per one unit' of Quantity B, divide Quantity A by Quantity B. The result will be 'some amount of A per 1 unit of B'.
Proportional Relationship Formula
y = kx
This formula models a linear relationship where 'k' is the unit rate (constant of proportionality). 'x' is the independent variable (e.g., number of items, hours) and 'y' is the dependent variable (e.g., total cost, total distance). This shows that the unit rate is the slope of the line.
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Challenging
A 2-liter bottle of juice costs $3.80. A 1.5-liter bottle costs $2.94. A new 0.75-liter bottle is introduced. What is the maximum price (rounded to the nearest cent) the 0.75-liter bottle can be for it to be the 'best buy'?
A.Less than $1.43
B.Less than $1.47
C.Less than $1.96
D.Less than $2.21
Challenging
The price of fuel in the USA is $3.50 per gallon. In Canada, it's $1.60 CAD per liter. Given the exchange rate 1 USD = 1.35 CAD and 1 gallon ≈ 3.785 liters, what is the approximate price of the Canadian gas in USD per gallon?
A.$3.50 / gallon
B.$4.49 / gallon
C.$5.21 / gallon
D.$6.05 / gallon
Challenging
A graph of a proportional relationship, y = kx, passes through the point (6, 15). A second process is 20% more efficient, meaning its unit rate is 20% higher. What is the equation for this second process?
A.y = 2.5x
B.y = 18x
C.y = 3x
D.y = 2.7x
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