As shown in the figure, the radius of the small circle is 4dm, and the shadow part accounts for 1 / 5 of the area of the small circle and 1 / 8 of the area of the large circle. How many square decimeters is the area of the large circle
1 / 5 of small circle area: 3.14 × 4 × 4 × 1 / 5 = 10.048 square decimeters
Large circle area: 10.048 △ 1 / 8 = 80.384 square decimeters