A square has a perimeter of 20 cm what is the length of its diagonal rounded to the nearest tenth

multiply the length of one side by the square root of 2.

20 √2 = 28.28

Rounded to the nearest tenth:

28.28 →28.3

28.3 is the final answer

- - All 4 sides of a square are the same length.

The perimeter is 20 cm.

So each side is (20/4) = 5 cm.

- - If you cut the square along its diagonal, and throw one piece away ...

You have a right triangle.

The legs are sides of the square ... 5 cm each.

The hypotenuse is the diagonal of the square, which you have to find.

- - The (hypotenuse of any right triangle) ²

= (the length of one leg) ² + (the length of the other leg) ².

(Diagonal) ² = (5 cm) ² + (5 cm) ²

(Diagonal) ² = (25 cm²) + (25 cm²)

(Diagonal) ² = (50 cm²)

Diagonal = √ (50 cm²) = 7.07 cm

or 7.1 cm rounded to the nearest tenth.