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Geometry H
Mrs. Diaz
NAME:_______________________________
DATE:_______________________________
UNIT 5
ASSIGNMENT #1
Introduction to Proportions
OBJECTIVE: S.W.B.A.T. set up proportions from a given prompt, then solve the proportion correctly using
cross multiplication.
THE LINK
Communicating what we know about: Solving Ratios and Proportions in Geometry
PROBLEM
VOCABULARY
Directions: Read and mark up the text.
About 15 of every 1000 light bulbs assembled at the
A ratio compares values.
Brite Lite Company are defective. If the Brite Lite
A proportion is a name we give to a statement
that two ratios are equal. two equal fractions,
Company assembles approximately 13,000 light
bulbs each day.
ALGEBRAIC
Set up a proportion to solve the problem. Let x
COMMUNICATION
Directions: Further connections to geometry.
represent the number of defective light bulbs per day.
Below is the proportion set up, describe each step
15
x

1000 13,000
15(13,000)  1000 x _____________________
195,000  1000 x
195,000
x
1000
195  x
_____________________
______________________
1. The ratio of width to length of a rectangle is 7
: 10. The width of the rectangle is 91 cm. Write
and solve a proportion to find the length.
2. The ratio of the two acute angles in a
right triangle is 5 : 13. What is the
measure of each angle in the right
triangle?
______________________
1. About how many are defective?
2. In most recent studies, the Bright Lite
Company has found that 22 out of 1243 light
bulbs were deffective. If the company assembles
the same approximate number of light bulbs a
each day, about how many are deffective now?
3. The ratio of the three angles of a
triangle is 2:3:4, find the measure of
each angle.
Ratios and Proportions: A Second Look
In a proportion, the products of terms that are diagonally across the
equal sign from each other are the same. This is called the Cross
Products Property because the products cross at the equal sign.
Proportions have other properties:
 Property (1)
a
b
 dc is equivalent to ba  dc .
Use reciprocals of the ratios.
 Property (2)
a
b
 dc is equivalent to
a
c
Switch b and c in the proportion.
 Property (3)
a
b
 dc is equivalent to
a b
b

b
d

cd
d
.
Add the denominator to the numerator.
Exercises
Use the proportion
x 2
= Complete each statement. Justify your answer.
10 z
1.
2.
3.
4. The ratio of width to length of a rectangle is 7 : 10. The width of the rectangle is 91 cm. Write and
solve a proportion to find the length.
5. The ratio of the two acute angles in a right triangle is 5 : 13. What is the measure of each angle in
the right triangle?
Algebra Solve each proportion.
x 13
6. 
4 52
7.
x
16

2 x  1 40
8.
x 6

Use the proportion z 5 . Complete each statement. Justify your answer.
9.
x

6
10.
xz

z
Coordinate Geometry Use the graph.
Write each ratio in simplest form.
11.
AB
BD
12.
AE
EC
13.
EC
BC
14.
slope of BE
slope of AE
9 9x

10 70