Transcript Document

What is a scale factor and how do
you compute one?
Happy
Town
Smile
City
Funville
Gladberg
Scale in miles:
1 inch = Approx. 15 miles
In this lesson you will learn
how to determine the scale
factor between two similar
figures by applying ratios.
Let’s
Review
Let’s
Review
A ratio is a comparison
between two numbers.
For example:
# Apples : # Oranges = 4 : 2 or 2 : 1
A Common
Let’s
Review Mistake
Reversing the order of the ratio
For example:
# Apples : # Oranges = 2 : 4 or 1 : 2
CoreReview
Lesson
Let’s
Two figures are similar if the lengths
of every pair of corresponding sides
are in the same ratio.
B
16
22
8
M
11
L
12
A
24
8
16
21
=
21
16
8
C
N
22
21
11
=
11
22
21
12 21
24
=
24
12 21
CoreReview
Lesson
Let’s
The scale factor is the ratio of the lengths
of corresponding sides in similar figures.
Q
T
4
4
S
W
R
Z
6
6
Y
X
23
4
Scale factor of small
large to small
large = 6
=
32
4
6
CoreReview
Lesson
Let’s
Scale factor on a map:
The number of
inches on the
map that
corresponds to
the actual
number of
miles
3 inches
45 miles
Smile
City
Happy
Town
Funville
Gladberg
Scale in miles:
1 inch = Approx.
15 miles
In this lesson you have
learned how to determine the
scale factor between two
similar figures by applying
ratios.
Guided
Practice
Let’s
Review
Find the scale factor of the small
triangle to the large triangle.
40
10
10
25
16
25
Extension
Let’s
ReviewActivities
Describe in words what it means when
a diagram is drawn in a 1:10 scale.
Extension
Let’s
ReviewActivities
Find the scale factor of triangle DEF
to triangle PQR.
E
9
Q
15
P
R
D
42
F
Perimeter of PQR = 42
Quick Quiz
Let’s
Review
1. Find the scale factor of the small
rectangle to the large rectangle.
32
80
12
30
Quick Quiz
Let’s
Review
2. Find the scale factor of the large
triangle to the small triangle.
A
26
B
M
14
N
L
45
C