Most of us are familiar with the conversion formula
![](../mgifs/gifs1/ctof.gif)
that converts Celsius temperatures to Fahrenheit. Since many of us have difficulty
doing fractions in our heads, an "alternate" method is taught to American travelers in Europe:
- Double the Celsius temperature.
- Subtract 10% of that value.
- Add 32.
Most of us can do these computations in our head!
For example, let C = 20 degrees.
Doubling it, we get 40.
Ten percent of 40 is 4.
Subtracting 4 from 40 is 36.
Adding 32 yields 68 degree Fahrenheit.
Using the formula
![](../mgifs/gifs1/ctof.gif)
we arrive at the same answer:
Why does this work?
This would be a good exercise for an Algebra I class to do
when they are studying combining like terms.