Math Quiz Scores

Question: Bobby's teacher gave him a math quiz. Every time he got an answer right, points would be taken away, so whoever had the most points, got the most questions wrong. Bobby's score was the highest, yet he still got the most questions correct out of the class. How is this possible?

Question: When is 99 more than 100?

Question: You have a glass of water that looks about half full. How can you tell, only using the glass of water itself, if the glass is half full or not?

The glass is a right cylinder.

Question: There is a 5 gallon and a 3 gallon box. You also have a hose with unlimited water. How are you gonna make the 5 gallon have 4 gallons using your items? (You do not know the exact measure measurements of a gallon)

Question: I'm 10 years old my brothers half my age now I'm 100 years old how old is my brother now?

Question: What are the next two letters in the following series and why? WATNTLITFS__