Which of the following is NOT a method to convert units of temperature?

The method of converting temperature units must adhere to established formulas that relate different temperature scales, such as Celsius, Fahrenheit, and Kelvin. The correct conversion methods involve specific arithmetic operations that maintain the integrity of the temperature values.

The method of adding 50 and then dividing by 2 does not correspond to any established conversion technique between temperature scales. In contrast, the other listed methods represent legitimate conversions. For example, subtracting 32 and then dividing by 1.8 is the formula used to convert Fahrenheit to Celsius, while adding 32 and multiplying by 1.8 is used to convert Celsius to Fahrenheit. Additionally, multiplying by 1.8 is part of the process for adjusting Celsius temperatures to Fahrenheit when used with the appropriate constants.

Thus, option A stands out as not fitting within the mathematical framework required for temperature conversion, making it the correct choice.