The area of a square with a side length of 20 meters. In daily life, the size of a jewelry store of more than 400 square meters is the area of a square with a side length of 20 meters. It is a little smaller than a basketball court. The basketball court is a rectangular plane. The basketball court is 28 meters long, 0/5 meters wide and 420 square meters in area, which is a little smaller than the area of a basketball court. The 400-square-meter storefront of the jewelry store is a big store. The jewelry store mainly sells gold jewelry, silver jewelry and pearl jewelry.