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Chapter 6—Expressions and Equations
66 Working With Formulas
When you complete the work for this section, you should be able to:  Describe the purpose of a formula.
 Demonstrate the use of formulas.

Definition A formula is a mathematical statement, or equation, that shows the exact relationship between two or more variables. 
A formula is very much like a set of instructions for converting variables into a solution. Here is an example of a formula that expresses distance traveled in terms of the average speed and time of travel. The formula looks like this:
d = st
where:
 d = the distance traveled
 s = the average speed
 t = the amount of time
If you know the speed and time of travel, the formula provides the exact instructions for finding the distance: multiply the speed by the time. It's simply a matter of evaluating the expression — a formula in this case.
Example
A car travels an average speed of 45 miles per hour for 4 hours. How far does it travel in that time?
 The desired formula is d = st.
 Substituting the known values: d = 45 x 4
 Doing the math: d = 180 miles.

The formula for converting Centigrade temperatures to Fahrenheit is:
F = 1.8C + 32
where:
 F = temperature in °F
 C = temperature in °C
Example
Express 50°C to Fahrenheit.
 The desired formula is F = 1.8C + 32°
 Substituting known values: F = 1.8(50) + 32
 Doing the math: F = 90 + 32 = 122
So: 50°C = 122°F