What is the length of the longest pole that can fit itself in a hall 60 feet long, 30 feet broad and 20 feet high?

70 feet

Length of diagonal of a cuboid = Length of the longest chord =$\sqrt {l^2 + b^2 + h^2}$

Here, hall has length = 60 feet ,

breadth = 30 feet

height = 20 feet 

So, length of the longest rod = $\sqrt {60^2 + 30^2 + 20^2}$= $\sqrt {4900}$ = 70 feet