Logic Riddles

Question: What single line can you add to the following statement to make it true?

5+5+5=550

Question: You are a prisoner. The only way to escape the prison is to walk down a very long hallway that takes 2 hours to get through. Guards come out of a door halfway down the hall every hour and take any prisoners walking out back to the prison and escort any visitors out of the prison. The guards cannot tell the difference between prisoners and visitors.

How do you escape?

Question: You fill up a bathtub with water and you have a teaspoon, tablespoon, and fourth cup. What is the fastest way to empty the bathtub?

Question: A person has one lion, one lamb and a bundle of grass. He wants to cross a river but there is only one boat and it can't sustain the weight of more than two articles at time. Also, he has to make sure that the lion doesn't eat the lamb and the lamb doesn't eat the grass. How will he get to the other side of the river with all three intact?

Question: There are 100 prisoners lining up to go to jail. Each prisoner is wearing a hat that is either black or white. The prisoners don't know their own hat color, just the hat color of those in front of them in line (the first prisoner in line can't see anyone's hat and the last prisoner can see everyone's hat except their own). Starting from the back, one of the guards asks each prisoner what color their hat is. If they are correct they get to go free but if they are wrong they go to jail.If the prisoners get to discuss a plan, how can at least 99 of them be saved?