The minimum and maximum temperatures for a crop on a given day are 13°C and 30°C, respectively. Calculate the Growing Degree Days (GDD) for the day if the base temperature for the crop is 5°C.

Growing degree days are also known as growing degree units are a heuristic tool in phenology. It is a measure of heat accumulation to predict plant and animal development rates such as the date that a flower will bloom, or a crop will reach maturity.
It is calculated by subtracting the plant’s lower base or threshold temperature of 50degree Fahrenheit from the average daily air temperature.
Here, $$\left[ {\frac{{\left( {13 + 30} \right)}}{2}} \right] - 5 = 16.5$$