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Evaluating expressions with variables: temperature

In this example we have a formula for converting Celsius temperature to Fahrenheit. Let's substitute the variable with a value (Celsius temp) to get the degrees in Fahrenheit. Great problem to practice with us! Created by Sal Khan and Monterey Institute for Technology and Education.

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Video transcript

Express 25 degrees Celsius as a temperature in degrees Fahrenheit using the formula Fahrenheit, or F, is equal to 9/5 times the Celsius degrees plus 32. So they're telling us that we have 25 degrees Celsius. So we could put that in for C here, and we'll get the temperature in Fahrenheit degrees. So let's do that. So we'll get F is equal to 9/5-- now for C, we're going to put in 25-- times 25 plus 32. And now we can simplify this before we multiply 25 times 9. Remember, this is the same thing as 9/5 times 25/1. We can essentially divide the numerator and the denominator of our eventual product by 5. If we divide 25 by 5, we get 5. If we divide 5 by 5, we get 1. So this boils down to 9 times 5 plus 32. So our Fahrenheit degrees are going to be 9 times 5 is 45 plus 32 degrees. Or it's equal to 45 plus 32 is 77, so this is 77 degrees Fahrenheit.