Mr Smith likes be exact.One day when he is walking in the street,a man comes over and asks him:"Excuse me ,but where's the nearest bookshop?" "The nearest bookshop You have to cross a bridge.and then turn to the right." "and is the bridge is long?" "very!thirty metres." the man thanks him and goes towards the bridge .suddenly he hears someone running after him ."shop!"Mr smith is shouting !"I'm sorry ,I just remember:the bridge is forty metres long .If you go thirty metres and then rurn to the right ,as I tell you to do ,you'll fall into the river."