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# Download Units - TTU Math Department

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Chapter 2A & 2B - Units and Conversion Factors Multiplication and Division of Units Operation Division Second power Third power Multiplication Keyword per squared cubed hypen Example miles/hours → “miles per hour” ft × ft or ft2 ft × ft × ft or ft3 kilowatt hours → “kilowatt-hours” Working with Units Step 1: Identify the units in the problem. Use the units to decide how to approach the solution and the units for the answer. Step 2: Perform operations (such as multiplication or division) on both numbers and units. But remember (a) You cannot add or subtract numbers with different units. But you can combine different units with multiplication, division or raising to a power. (b) Often it is easier to work with the reciprocal of an expression. Step 3: Always keep checking units to make sure you are working with the correct units. Standardized Units U.S. and Metric 1. International Metric System Main system used around the world. Also known as the SI (Système International d’Unités) 2. United States still also uses the U.S. Customary Systems (USCS) also sometimes called the English System. (See Table 2.2 - 2.6) Units of Density and Concentration 1. Density describes compactness or crowding; 2. Material density given in units of mass per unit volume; i.e., g/cm3; 3. Population density given by the number of people per unit area; 4. Information density how much information can be stored by digital media. 1. Concentration describes the amount of one substance mixed with another; 2. Concentration of an air pollutant measured by the number of molecules of the pollutant per million molecules of air; 3. Blood alcohol content measured in units of grams of alcohol per 100 milliliters of blood. Conversion Factors