What is the area of a rectangle if its fourth part is 20 dm2.

Let us denote the entire area of ​​the rectangle by the variable x.

If one quantity is the nth part of another quantity, then this quantity is equal to the product of that quantity and the number n. Thus, you can compose the equality:

x * 1/4 = 20.

The resulting equality is an equation with one variable. Such an equation can be solved by expressing the variable on the left side of the equality, using the main property of proportion – crosswise.

Let’s solve the resulting linear equation with one variable:

(x * 1) / 4 = 20;

x / 4 = 20;

x = (4 * 20) / (1 * 1);

x = 80/1;

x = 80 dm ^ 2.

Answer: if 1/4 of the area of ​​the rectangle is 20 dm ^ 2, then this area is 80 dm ^ 2.