6th Grade Math Textbook, Fundamentals

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2-9

Find wwhen P44 cm and 13 cm.

Solve:P 2  2 w

44 2(13)  2 w Substitute the known values.

44  26  2 w Simplify.

44  26  26  26  2 w Use the Subtraction Property of Equality.

18  2 w Simplify.

18  2  2 w 2 Use the Division Property of Equality.

9 w

Check: 44 2(13)  2 w

44 2 • 13 2 • 9 Substitute 9 for w.

44 26  18

44  44 Tr u e

So the width is 9 cm.

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(^1) Remember:
Perimeter of a Rectangle:
P 2  2 w
or
P2(w)
w
13 cm
Formulas
Objective To find missing values in problems involving formulas
A terrarium is 60 centimeters long, 30 centimeters wide,
and 40 centimeters tall. What is the volume, in cubic
centimeters, of the terrarium?
To find how many cubic centimeters of space is inside
the terrarium, use the formula for the volume of a
rectangular prism.

A is an equation, or rule, that shows

a mathematical relationship between two or

more quantities.

Each variable in the formula represents a part of the

problem that can change. Each constant represents

a number that does not change.

Use the formula for the volume of a rectangular prism.

Volume length width height

V   • w • h

60 cm • 30 cm • 40 cm Substitute the numbers given. Then solve.

72,000 cubic centimeters

The volume of the terrarium is 72,000 cubic centimeters.

You can use formulas to find missing dimensions of figures.

For Examples 1 and 2, use the formula for the perimeter of a rectangle.

formula