Evaluating expressions with variables: temperature
About this video
The video uses the formula F = 9/5 x C + 32 to change 25 degrees Celsius into Fahrenheit. It substitutes 25 for C, simplifies 9/5 x 25 by dividing 25 and 5 by 5 to get 9 x 5 = 45, then adds 32 to get 77 degrees Fahrenheit.
You'll be able to
- substitute a value into a formula to evaluate it.
- simplify a fraction times a whole number by dividing before multiplying.
- convert a temperature from Celsius to Fahrenheit using a formula.
Key words
- formula
- A rule written with variables that tells you how to work something out, like F = 9/5 x C + 32.
- Celsius
- A temperature scale where water freezes at 0 degrees.
- Fahrenheit
- A temperature scale used in the US where water freezes at 32 degrees.
- substitute
- Replace a variable with the number it stands for.
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.
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