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.