Reduce one side of a square by 20% and increase the other side by 2m to get a rectangle. This rectangle has the same area as the original square So what's the area of the original square? It's best to solve it by column arithmetic

Reduce one side of a square by 20% and increase the other side by 2m to get a rectangle. This rectangle has the same area as the original square So what's the area of the original square? It's best to solve it by column arithmetic

Idea: the original square area a * a, to make the area of the rectangle equal to the original square area, and one side reduces by 20%, that is, the original 80%, the other side increases by a quarter, that is, the original 5 / 4, because a × 4 / 5 × a × 5 / 4 = a * a