To find the length of a computer keyboard, we can use a ruler. On a ruler, the metric units are usually centimeters, often abbreviated as $(cm) .$

Extra

Metric Units of Length

We will review what we know about metric units of length. Let's start by taking a look at the table below which shows different units.

Metric Units of Length
$1$ kilometer = $1000$ meters
$1$ meter = $100$ centimeters
$1$ centimeter = $10$ millimeters

Note that when we need to convert from smaller to larger units, we multiply. When we want to convert from larger to smaller units, we divide. Now let's assume that we measured our keyboard and found that it is $40$ centimeters long.

We will convert this measure to both larger and smaller metric units. Let's begin with the smaller unit, millimeters. Notice that there are

10

millimeters in each centimeter.

40 cm \times 10 = 400 mm

We found that our keyboard is

400

millimeters long. Now let's convert

40

centimeters to kilometers, which are considerably larger than centimeters. To do so, we need to first change centimeters to meters. Since

1

meter is

100

centimeters, we need to divide by

100 .

40 cm \div 100 = 0.4 m

Next, because there are

1000

meters in

1

kilometer, we can change meters to kilometers by dividing the result by

1000 .

0.4 m \div 1000 = 0.0004 km

Finally, we found that our keyboard is

400

millimeters, or

0.0004

kilometers, long.

Exercise