Page 187 - Math Course 1 (Book 1)

Proportions

Mo. 6

Lesson 3 Key Concept

KEY CONCEPTS: Proportion
1. Solve proportions.
2. Use proportions to solve real-world Words A proportion is an equation stating that
problems. two ratios or rates are equal.

a c 2 6
Symbol = Example =
b d 3 9
MO. 6 - L3a

Solving Proportions Property of Proportion

Words The cross products of a proportion are
equal.
Vocabulary A-Z a c
=
Let us learn some vocabulary Symbol if , then ad = bc. If ad = bc,
d
b
a
c
then = is proportional
b d
Proportion
Let’s Begin
When two ratios are equal they form a proportion

2 6 25 1
= = Solve Proportions
3 9 100 4

Examples

Cross Products
c 9
Solve the proportion =
can be used to determine whether two ratios form a 36 15
proportion.
c 9
12(168) is 84(24) is 36 = 15
one cross 12 24 another
product. = cross c • 15 = 36 • 9 Cross products
84 168 product.
15c = 324 Multiply.
12(168) = 84(24) 15c = 324 Divide

15 15
2016 = 2016 c = 21.6
The cross products are equal.

The cross products of any proportion are equal. Answer The solution is 21.6

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