Here's one that took me a while when I first heard it.

A man walks up to two unmarked doors, each with a doorman. There is a sign between the doors saying "One of these doors will bring you great pleasure, the other will give you great pain. One of the attendants will lie, one will tell the truth. You may ask one question for both to answer."

What question should the man ask to find out the good door?

Remember: only one question which both will answer.

Which door would the other man tell me will bring me great pleasure?
Truth teller will tell you the pain door because that is what the liar would tell you.
The liar will also tell you the pain door because the truth teller would say the pleasure door but he has to lie and tell you the other door.

Which door would the other man tell me will bring me great pleasure?
Truth teller will tell you the pain door because that is what the liar would tell you.
The liar will also tell you the pain door because the truth teller would say the pleasure door but he has to lie and tell you the other door.

The following will reveal your age and number of children

Grab a calculator (You wonâ€™t be able to do this one in your head)
Enter your current age into the calculator
Multiply by 2
Add 5
Multiply by 50
Subtract 365
Add the number of children you have (0 if you have no kids)
Add 115
The first two digits of the result should be your age and the last two digits should be the number of kids you have.

Romeo and Juliet are found dead on the floor in a bedroom. On the floor is glass and water. The only furniture in the room is a bed and a shelf. There is nothing near the house except for a railroad track. What caused the death of Romeo and Juliet?

Now will they? I have my doubts. Here in Belgium, we have one of the most dense road maps of the world.
Traffics jams, road constructions, pits in the road ...