Page 75 - Basic College Mathematics with Early Integers

52 C HAPTE R 1 I THE WHOLE NUMBERS

PRACTICE 8–9 Examples Multiply.

Multiply. 8. 25 9000=225,000 4 25
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8. 35 3000 * 9 Attach 3 zeros.
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9. 600 600
225
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9. 20 7000 = 140,000 Attach 4 zeros.
2
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2 7
Work Practice 8–9

Objective Finding the Area of a Rectangle
A special application of multiplication is finding the area of a region. Area mea-
sures the amount of surface of a region. For example, we measure a plot of land or
the living space of a home by its area.The figures below show two examples of units
of area measure. (A centimeter is a unit of length in the metric system.)

Actual size

Actual size
1 square 1 square
1 inch 1 centimeter
inch cm
1 centimeter

1 inch

For example, to measure the area of a geometric figure such as the rectangle
below, count the number of square units that cover the region.

1 square
How many of these are in this? 3 centimeters
cm

4 centimeters

This rectangular region contains 12 square units, each 1 square centimeter.Thus, the
area is 12 square centimeters. This total number of squares can be found by count-
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ing or by multiplying 4 3 (length width).
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Area of a rectangle = length width
= (4 centimeters)(3 centimeters)
= 12 square centimeters
Copyright 2012 Pearson Education, Inc.
In this section, we find the areas of rectangles only. In later sections, we will find
the areas of other geometric regions.

Answers Notice that area is measured in square units while perimeter is measured in units.
8. 105,000 9. 360,000