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Measurement: GED Test Prep (page 5)

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Updated on Mar 9, 2011

Basic Operations with Measurement

It will be necessary for you to review how to add, subtract, multiply, and divide with measurement. The mathematical rules needed for each of these operations with measurement follow.

Addition with Measurements

To add measurements, follow these two steps:

  1. Add like units.
  2. Simplify the answer.

4 pounds 25 ounces =

4 pounds + 1 pound 9 ounces =

5 pounds 9 ounces

Subtraction with Measurements

To subtract measurements, follow these three steps:

  1. Subtract like units.
  2. Regroup units when necessary.
  3. Write the answer in simplest form.

Sometimes, it is necessary to regroup units when subtracting.

    Example: Subtract 3 yards 2 feet from 5 yards 1 foot.
    From 5 yards, regroup 1 yard to 3 feet. Add 3 feet to 1 foot. Then, subtract feet from feet and yards from yards.

Multiplication with Measurements

To multiply measurements, follow these two steps:

  1. Multiply like units if units are involved.
  2. Simplify the answer.

Example: Multiply 9 feet by 4 yards. First, change yards to feet by multiplying the number of feet in a yard (3) by the number of yards in this problem (4).

    3 feet in a yard × 4 yards = 12 feet

Then, multiply 9 feet by 12 feet = 108 square feet.

(Note: feet × feet = square feet)

Division with Measurements

For division with measurements, follow these steps:

  1. Divide into the larger units first.
  2. Convert the remainder to the smaller unit.
  3. Add the converted remainder to the existing smaller unit if any.
  4. Divide into smaller units.
  5. Write the answer in simplest form.

Metric Measurements

The metric system is an international system of measurement also called the decimal system. Converting units in the metric system is much easier than converting units in the English system of measurement. However, making conversions between the two systems is much more difficult. Luckily, the GED will provide you with the appropriate conversion factor when needed. The basic units of the metric system are the meter, gram, and liter. Here is a general idea of how the two systems compare:

Prefixes are attached to these basic metric units to indicate the amount of each unit.

For example, the prefix deci- means one-tenth (); therefore, one decigram is one-tenth of a gram, and one decimeter is one-tenth of a meter. The following six prefixes can be used with every metric unit:

Examples

  • 1 hectometer = 1 hm = 100 meters
  • 1 millimeter = 1 mm = meter = .001 meter
  • 1 dekagram = 1 dkg = 10 grams
  • 1 centiliter = 1 cL* = liter = .01 liter
  • 1 kilogram = 1 kg = 1,000 grams
  • 1 deciliter = 1 dL* = liter = .1 liter

*Notice that liter is abbreviated with a capital letter—L.

The following chart illustrates some common relationships used in the metric system:

Conversions within the Metric System

An easy way to do conversions with the metric system is to move the decimal point either to the right or left because the conversion factor is always ten or a power of ten. As you learned previously, when you change from a large unit to a smaller unit you multiply, and when you change from a small unit to a larger unit you divide.

Making Easy Conversions within the Metric System

When you multiply by a power of ten, you move the decimal point to the right. When you divide by a power of ten, you move the decimal point to the left.

To change from a large unit to a smaller unit, move the decimal point to the right.

To change from a small unit to a larger unit, move the decimal point to the left.

Example

Change 520 grams to kilograms.

Step 1: Be aware that changing meters to kilometers is going from small units to larger units; therefore, you will move the decimal point three places to the left.

Step 2: Beginning at the UNIT (for grams), you need to move three prefixes to the left.

Step 3: Move the decimal point from the end of 520 to the left three places:

Place the decimal point before the 5.

Your answer is 520 grams = .520 kilograms.

Example

You are packing your bicycle for a trip from New York City to Detroit. The rack on the back of your bike can hold 20 kilograms. If you exceed that limit, you must buy stabilizers for the rack that cost $2.80 each. Each stabilizer can hold an additional kilogram. If you want to pack 23,000 grams of supplies, how much money will you have to spend on the stabilizers?

Step 1: First, change 23,000 grams to kilograms.

Step 2: Move the decimal point three places to the left:

    23,000 g = 23.000 kg = 23 kg

Step 3: Subtract to find the amount over the limit:

    23 kg – 20 kg = 3 kg

Step 4: Because each stabilizer holds 1 kilogram and your supplies exceed the weight limit of the rack by 3 kilograms, you must purchase 3 stabilizers from the bike store.

Step 5: Each stabilizer costs $2.80, so multiply $2.80 by 3:

    $2.80 × 3 = $8.40
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