Centigrade (Celsius) to Fahrenheit:
e.g. 10° = 50° as 10*9, 90/5 = 18, 18+32 = 50
Fahrenheit to Centigrade (Celsius):
e.g. 50°F = 10° as 50 - 32 = 18*5 = 90, 90/9 = 10