Wind chill
According to the National Climatic Data Center, during 1991, the lowest temperature recorded in Indianapolis, Indiana, was 0°F. If x is the wind speed in miles per hour and x ≥ 5, then the wind chill (in degrees Fahrenheit) for an air temperature of 0°F can be approximated by the function
(a) At what rate is the wind chill changing when the wind speed is 20 mph?
(b) Explain the meaning of your answer to part (a).