Lesson 3.4b Solving Proportions.notebook
October 12, 2012
The length of a rectangle is 6 in more
than its width. The perimeter of the
rectangle is 24 in. What is the length
of the rectangle?
3.4 Solving Proportions
Objective: Be able to set up and use proportions
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Lesson 3.4b Solving Proportions.notebook
October 12, 2012
A ratio is a comparison of two numbers
a to b
a : b
a
b
Examples: "I got 21 out of 24 questions correct."
21 to 24 21:24
21 24
A ratio is a comparison of two numbers
a : b
a to b
a
b
1. 23 out of 30 students got an A on the test
2. A canary's heart beats 200 times in 12 seconds
3. You traveled 186 miles in 3 hours 2
Lesson 3.4b Solving Proportions.notebook
October 12, 2012
A proportion is an equation that states that two ratios are equal
"a is to b as c is to d"
a c
=
b d
A proportion is solved by cross multiplication
(multiply diagonally)
a c
=
b d
ad = cb
2 ? 8
=
3 12
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Lesson 3.4b Solving Proportions.notebook
October 12, 2012
A proportion is solved by cross multiplication
(multiply diagonally)
a c
=
b d
ad = cb
1.
x 5
=
8 6
2.
y 4
=
12 7
3.
50 15
=
18 m
Jennifer estimates that two out of every three students in her class will attend the class party. How many students out of 750 in her class can you predict will attend?
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Lesson 3.4b Solving Proportions.notebook
October 12, 2012
Jordan can text 25 letters in 10 seconds. How many seconds will it take him to text 20 letters?
Solve the proportions:
Example 1:
Example 2:
3 = x ­ 3
6
8
3 = 5
w + 6 w ­ 4
5