Algebra  K11The formula for converting a Celsius temperature (C) to a Fahrenheit temperature (F) is given by

F = (9/5) x C + 32

There is a simple approximation: You double C and add 30.

The error in the approximation varies from 2°F to 6°F in the range of -20°C to +20°C.

What is the Celsius temperature when the approximation is exact?