The length of the longest stick that can be fitted in a cubical vessel having an edge of length 20 cm, is _______.

$20\sqrt{3} $ cm

We know that,

Diagonal of cube = \(\sqrt {3}\) × Side of cube

We have,

Side = 20

The length of the longest stick that can be fitted in a cubical vessel is equal to the length of the diagonal of the cube.

The  length of the diagonal of the cubical vessel = \(\sqrt {3}\) × 20 = 20\(\sqrt {3}\)cm