A policeman goes 20 metres towards South and then turns to his right and walks 40 metres. He again turns to his left and walks 10 metres. How far is he now from his starting point?

He is 50 metres from the start.

South 20, then a right turn faces west for 40, then a left turn faces south for 10.

Net south = 20 + 10 = 30 metre.

Net west = 40 metre.

Distance = root(30 x 30 + 40 x 40) = root 2500 = 50 metre.