Final answer:
The farmer can spray 25 acres with one full tank.
Step-by-step explanation:
To calculate the number of acres the farmer can spray with one full tank, we need to divide the capacity of the tank (500 gallons) by the rate of application (20 gallons per acre). This gives us:
Number of Acres = Capacity of Tank / Rate of Application
Number of Acres = 500 gallons / 20 gallons per acre
Number of Acres = 25 acres
Therefore, the farmer can spray 25 acres with one full tank.