Good Riddles

Question: Which tables do you not have to learn?

Question: What kind of keys won't open a door?

Question: What does everyone always overlook?

Question: If 1+1=4, 7-3=2, and 5x2=8, then what is half of 19?

Question: I run, I save people, and I was hit by lightning, And my public name starts with an "F"