Final answer:
The area of the square is 100 square units.
Step-by-step explanation:
To find the area of a square, we need to know the length of its side. Let's call the length of the side x. According to the given information, the length of the square is 20 less than 5 times its length, which can be expressed as x = 5x - 20. Solving this equation, we find that x = 10.
Therefore, the area of the square is x * x = 10 * 10
= 100 square units.