Good Riddles

Question: Looking at my face, I'm no more than six.
Look at the rest of me and I'm 21.
You'll see my twin and me in Las Vegas.
Say my name and you'd be uttering a threat.

What am I?

Question: A prison has 23 prisoners in 23 different cells. The prisoners have no way to communicate with each other in any way from their cells. There is another room, the rec room, that has two switches on the wall (A and B). The switches have on and off positions but they start in an unknown position.

Prisoners are randomly taken to and from the rec room one at a time. They must change the position of only one of the two switches each time they go to the room. At any point a prisoner can yell out, "Every prisoner has been here!" If the prisoner is correct that all of the prisoners have visited the rec room, then they all go free. If they aren't correct then they are all executed.

Before they start they are given one planning session during which they can discuss a method to win the game. What method can they use to ensure they all go free?

Question: Say you roll five dice and get a one, a two, a three, a four, and a five. Your sum would be six. Rolling all threes would give ten. Rolling a two, four, two, four, and six would be zero. Rolling a two, three, four, five, and six would be six.

What would you get if you roll a three, a four, a one, a five, and a four?

Question: There are 6 sisters. Each sister has 1 brother. How many brothers are in the sisters' family?

Question: How much does the brick weigh if a brick weighs 1kg plus a half brick?