Question 886692
Area of a circle is Pi R squared.
At full pressure, the sprinkler covers Pi 4 squared (radius = 1/2 diameter) or 16 Pi.
At half pressure, assuming it covers half the distance, the sprinkler area is Pi 2 squared, or 4 Pi.
Therefore, at half pressure, the area of coverage is 12 Pi less.  4 Pi is 25% of 16 Pi, so reducing the pressure by 50% reduces the coverage area by 75%.