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# Two-Step Equations and Properties of Equality

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Taking Temperatures
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Credit: Liz West
Source: http://www.flickr.com/photos/53133240@N00/3201760894/

If you’re watching the news and the meteorologist says that it’s going to be 30 degrees outside, how would you dress? Does the answer change if you’re visiting Italy? It should! 30 degrees in the U.S. is winter coat weather, but 30 degrees in Italy means shorts and a T-shirt. Why? Because the countries use two different scales of temperature.

#### Freezing, Boiling, and Everything In Between

The United States uses the Fahrenheit scale to measure temperature. On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. 98.6 degrees is the human body temperature, and 30 degrees is a chilly winter day with a chance of snow. The Celsius scale sets the freezing point of water at 0 and the boiling point of water at 100. You can convert    between the scales by solving a two-step equation: $C = \frac{5(F-32)}{9}$. For example, you can figure out what 30°C is in degrees Fahrenheit by solving the following equation:

$C & = \frac{5(F-32)}{9}\\270 & = 5(F-32)\\54 & = F-32\\86 & = F$

So, 30°C is equivalent to 86°F, or a hot summer day.

Credit: Laura Guerin
Source: CK-12 Foundation

Most scientists use a third temperature scale: the Kelvin scale. 0 degrees Celsius is 273 degrees on the Kelvin scale. 0 on the Kelvin scale is absolute zero, the coldest temperature possible. The temperature in space is about 2.73 K. Scientists working in labs have tried to reach temperatures very close to absolute zero, and they’ve made some fascinating discoveries.