proportions.notebook
December 16, 2011
Lesson #40: Proportions
Aim: How do we work with proportions?
Do Now: Tammy travels 15 miles to school in 30 minutes. Mark goes to the same school but travels 20 miles to school in 40 minutes. Do they travel at the same rate? Show work to prove your answer.
aim/do now
A proportion is an equation stating that two ratios are equal.
15 = 20 30 40
definition
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proportions.notebook
December 16, 2011
15 miles = 20 miles 30 minutes 40 minutes
OR
15 miles = 30 minutes 20 miles 40 minutes
**When writing proportions, the order of the units used in the ratios must be the same.
units!
If 5 grams of gold costs $400, how much does 9 grams cost?
1) Set up a proportion
2) Cross multiply
3) Solve for the variable
cross­product
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proportions.notebook
December 16, 2011
Practice: Determine if each is a proportion.
2. 24/4 ≟ 60/5
1. 2/10 ≟ 5/25
3. 18/1 ≟ 36/3
Solve for the variable using the cross­product rule.
5. 3/7 = 15/d
4. 4/5 = x/20
6. 2/8 = t/14
practice
How long will it take a car traveling at a rate of 50 miles per hour to go 450 miles?
closing
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