A fountain takes the shape of a half sphere with diameter 10 feet that sits, flat side down, in the center of a round brick-paved patio of diameter 100 feet. What is the area of the portion of the patio that is left uncovered?
1. Check the picture below. It illustrates an upper view of the fountain, which forms a circle with radius 5 ft, and the patio, with radius equal to 50 ft.