Given that,
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.
Solution,
The high temperature was 51°F and the low temperature was 45°F.
Average of high and low temperatures for the day is given by :
[tex]T=\dfrac{51+45}{2}\\\\T=48^{\circ} F[/tex]
Now using formula :
H = 65 - T
H = 65 - 48
H = 17
Hence, there are 17 heating degree days.