What is the area of the rectangle if the fourth part of it is equal to 20 dm2?

To solve this problem, you need to make a proportion.
Since the area of the fourth part of the rectangle is 20 decimeters squared, it follows that we can find the area by multiplying the number of parts 4 by the area of one part of 20 decimeters squared.
Let us write down in numerical form.
4 * 20 = 80 dm2
Thus, the area of the entire rectangle will be 80 decimeters squared.
Answer 80 dm2

you can also determine the area through proportion, where 1/4 * 20 = 1 * x
In this case, we also get 80 dm2