A13­4RatioProportion.notebook
September 25, 2015
Algebra 1
Ch.3 Notes Page 21
P21 3­4 Ratio and Proportion
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Ratios and Rates
A ratio is a comparison of two numbers by division. a to b ; a:b ; a/b ; 2/3
A rate is a ratio that uses 2 different units
Dollars/Ounces
A UNIT rate is a rate with a denominator of 1. $.72/16oz = $.045/1oz
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A13­4RatioProportion.notebook
September 25, 2015
In 2004, Lance Armstrong won the Tour de France, completing the 3,391 km course in about 83.6 hours. Find Lance's unit rate. Cycling at his average speed, about how long would it take Lance to cycle 185 km?
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Proportions
A proportion is an equation that states that two ratios are equal.
A = C
B D
AD = BC
5 = 10
8 16
AD = BC
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A13­4RatioProportion.notebook
September 25, 2015
To Solve Proportions...
Cross Multiply and Divide
4 = 12
x = 10
5 x
8 16
Are these Proportional???
3 = 10
8 11
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Solving Multi­step Proportions...
Cross Multiply and Divide
3 = 5 x + 6 x ­ 4
x + 4 = x ­ 2
5 7
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