Q.
there are six eggs in the basket.
six people each take one egg.
how can it be that one egg is left in the basket?

Q.
acting on an anonymous phone call,
the police raid a house to arrest a suspected murderer.
they don't know what he looks like,
but they know his name is John.
inside they find a carpenter, a lorry driver, a car mechanic and a fireman play cards.
without even asking his name,
they immediately arrest the fireman.
how do they know they've got their man?