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Have you ever run a 5 k or 10 k race? The lengths of those races are measured in kilometers. The metric system is commonly used in the United States when talking about the length of a race.

Nick ran a 10-kilometer race. How many meters did he run?

A photograph of 8 male runners in a track race.
(credit: William Warby, Flickr)

Solution

We will convert kilometers to meters using the Identity Property of Multiplication and the equivalencies in [link] .

10 kilometers
Multiply the measurement to be converted by 1. .
Write 1 as a fraction relating kilometers and meters. .
Simplify. .
Multiply. 10,000 m
Nick ran 10,000 meters.

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Sandy completed her first 5-km race. How many meters did she run?

5000 m

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Herman bought a rug 2.5 meters in length. How many centimeters is the length?

250 cm

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Eleanor’s newborn baby weighed 3200 grams. How many kilograms did the baby weigh?

Solution

We will convert grams to kilograms.

.
Multiply the measurement to be converted by 1. .
Write 1 as a fraction relating kilograms and grams. .
Simplify. .
Multiply. .
Divide. 3.2 kilograms
The baby weighed 3.2 kilograms.

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Kari’s newborn baby weighed 2800 grams. How many kilograms did the baby weigh?

2.8 kilograms

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Anderson received a package that was marked 4500 grams. How many kilograms did this package weigh?

4.5 kilograms

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Since the metric system is based on multiples of ten, conversions involve multiplying by multiples of ten. In Decimal Operations , we learned how to simplify these calculations by just moving the decimal.

To multiply by 10 , 100 , or 1000 , we move the decimal to the right 1 , 2 , or 3 places, respectively. To multiply by 0.1 , 0.01 , or 0.001 we move the decimal to the left 1 , 2 , or 3 places respectively.

We can apply this pattern when we make measurement conversions in the metric system.

In [link] , we changed 3200 grams to kilograms by multiplying by 1 1000 ( or 0.001 ) . This is the same as moving the decimal 3 places to the left.

Multiplying 3200 by 1 over 1000 gives 3.2. Notice that the answer, 3.2, is similar to the original value, 3200, just with the decimal moved three places to the left.

Convert: 350 liters to kiloliters 4.1 liters to milliliters.

Solution

We will convert liters to kiloliters. In [link] , we see that 1 kiloliter = 1000 liters .

350 L
Multiply by 1, writing 1 as a fraction relating liters to kiloliters. .
Simplify. .
Move the decimal 3 units to the left. .
0.35 kL

We will convert liters to milliliters. In [link] , we see that 1 liter = 1000 milliliters.

4.1 L
Multiply by 1, writing 1 as a fraction relating milliliters to liters. .
Simplify. .
Move the decimal 3 units to the left. .
4100 mL

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Convert: 7.25 L to kL 6.3 L to mL.

  1. 7250 kL
  2. 6300 mL

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Convert: 350 hL to L 4.1 L to cL.

  1. 35,000 L
  2. 410 cL

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Use mixed units of measurement in the metric system

Performing arithmetic operations on measurements with mixed units of measures in the metric system requires the same care we used in the U.S. system . But it may be easier because of the relation of the units to the powers of 10 . We still must make sure to add or subtract like units.

Ryland is 1.6 meters tall. His younger brother is 85 centimeters tall. How much taller is Ryland than his younger brother?

Solution

We will subtract the lengths in meters. Convert 85 centimeters to meters by moving the decimal 2 places to the left; 85 cm is the same as 0.85 m.

Now that both measurements are in meters, subtract to find out how much taller Ryland is than his brother.

1.60 m −0.85 m _______ 0.75 m

Ryland is 0.75 meters taller than his brother.

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Source:  OpenStax, Prealgebra. OpenStax CNX. Jul 15, 2016 Download for free at http://legacy.cnx.org/content/col11756/1.9
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