Cut out the largest circle from a square sheet of iron with a side length of 20 cm. What percentage of the area of the remaining sheet of iron is the area of the original square?

Cut out the largest circle from a square sheet of iron with a side length of 20 cm. What percentage of the area of the remaining sheet of iron is the area of the original square?

What is the radius of the circle
20 △ 2 = 10 cm
What is the area of a circle
10 × 10 × 3.14 = 31 square centimeter
What is the area of a square
20 × 20 = 400 square centimeter
What is the utilization rate of this square sheet of iron
314÷400×100%=78.5%