7th Grade Math

Lesson 2B Scale Drawings and Models 285

a. MAPS On the map of Arkansas shown, find the actual distance

between Clarksville and Little Rock. Use a ruler to measure.

40

40





Little Rock

Clarksville

ARKANSAS

20 mi

0 1 cm

Use a Scale Model

PHONES A graphic artist is creating an

advertisement for a new cell phone. If she

4 in.

ABC 2

SPEAKER

DEF 3

JKL 5 MNO 6

TUV 8

+ 0

GHI 4

TALK END

PQRS 7

Shift*

WYXZ 9

Space#

1

BACK

uses a scale of 5 inches = 1 inch, what is

the length of the cell phone on the

advertisement?

Write a proportion using the scale. Let a

represent the length of the advertisement

cell phone.

Scale Length

advertisement

actual

_5 inches

1 inch

= _a inches

4 inches

advertisementactual

5 · 4 = 1 · a Cross products

20 = a Multiply.

The length of the cell phone on the advertisement is 20 inches long.

b. SCOOTERS A scooter is 3 _^1

2

feet long. Find the length of a scale

model of the scooter if the scale is 1 inch = _^3

4

feet.

A scale written as a ratio without units in simplest form is called the

scale factor.

scale

_^14 inch

_

2 feet

=

_^14 inch

_

24 inches

Convert 2 feet to 24 inches.

= _^4

4

·

_^14 inch

_

24 inches

Multiply by^4 _ 4 to eliminate the

fraction in the numerator.

Divide out the common units.

= _^1

96

scale factor

Scale Scale A map scale can be

written in different ways,

including the following:

1 cm = 20 mi

1 cm : 20 mi

_1 cm

20 mi^

Scale Scale The scale is the

ratio of the drawing/model

measure to the actual

measure. It is not always the

ratio of a smaller measure

to a larger measure.

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