In order to evaluate energy demand for heating services, the number of heating degree days are calculated. The number of heating degree days can be calculated by the formula H = 65 - T, where 65 is degrees Fahrenheit, and T is the average of the high and low temperatures for the day. If the high temperature for a day was 52°F and the low temperature for the same day was 45°F, what is the number of heating degree days?

First, we calculate the average of the high ([tex]T_{H}[/tex]) and low temperatures of the day ([tex]T_{L}[/tex]), measured in degrees Fahrenheit. If we know that [tex]T_{H} = 52\,^{\circ}F[/tex] and [tex]T_{L} = 45\,^{\circ}F[/tex], then the average temperature ([tex]T[/tex]), measured in degrees Fahrenheit, is:

[tex]T = \frac{T_{L}+T_{H}}{2}[/tex] (1)

[tex]T = \frac{45\,^{\circ}F+52\,^{\circ}F}{2}[/tex]

[tex]T = 48.5\,^{\circ}F[/tex]

And the number of heating days is:

[tex]H = 65-48.5[/tex]

[tex]H = 16.5[/tex]

The number of heating degree days is 16.5.