Write Ratios and Proportions

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Write Ratios and Proportions

• Algebra 1

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What is ratio?
Ratio uses division to compare two quantities.
You can write the ratio in three ways
a to b
a b
Each ratio is read the ratio of a to b. Ratios
needs to the in simplest form.
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Ex 1 Write a ratio
In Ms. Trans Algebra 1 class, there are 18 girls
and 16 boys. a. Find the ratio of girls to
boys b. Find the ratio of boys to the whole
class
girls
18
? 2
9
a.


16
boys
? 2
8
16
boys
? 2
8
16
b.



1816
17
34
whole class
? 2
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What is proportion?
Proportion is an equation that states that two
ratios are equivalent.
where b ? 0, d ? 0
To solve proportions we use the Cross Product.
(a)(d)

(b)(c)
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Ex 2 Solve the proportion
(5)(x)
(2)(10)
20 5x
5
5
4 x
(9)(10)
(k)(18)
18k 90
18
18
k 5
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Ex 3 Write the sentence as a
proportion and solve
3 is to 2 as x is to 6.
(3)(6)
(2)(x)
2x 18

2
2
x 9
x is to 10 as 7 is to 5.
(10)(7)
(x)(5)
5x 70

5
5
x 14
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Ex 4 Solve the following proportion
(5)(4x)
(2)(50)
100 20x
20
20
5 x
(x)(8)
(4)(x 3)
4x 12 8x
-4x
-4x
-12 4x
4
4
-3 x
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Assignment

• Students do page 165 (4-34) even.
• There will be a Warm-Up on this topic the next
  day.

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Reference

• Larson, Boswell, Kanold, and Stiff. Algebra I.
  2007. Houghton Mifflin Company.