Final answer:
The side length of the square is approximately 4.472 cm when rounded to the nearest tenth.
Step-by-step explanation:
To estimate the side length of a square with an area of 20 cm², we need to find the square root of 20. Let's use a calculator to find the approximate value: √20 ≈ 4.472. So, the side length of the square is approximately 4.472 cm when rounded to the nearest tenth.