根据短文内容，回答下列问题。

    Once there lived a very exact man. One day when he was walking in the street, an old woman came over and asked him, "Excuse me, but where's the nearest restaurant?"

    "The nearest restaurant? You have to cross a bridge and then turn to the right," answered the man.

    "And is the bridge long?"

    "Very, thirty metres."

    The old woman thanked him and went towards the bridge, Suddenly she heard someone running after her. "Stop!" the man was shouting. "I'm very sorry. I just remembered the bridge is forty metres long. If you go thirty metres and then turn to the right, as I told you to do, you will fall into the river.