You stand in front of two doors. A guard stands next to each door. You know the following things: one path leads to paradise, the other leads to death. You cannot distinguish between the two doors. You also know that one of the two guards always tells the truth and the other always lies. You have permission to ask one guard one question to discover which door leads to paradise. What one question would you ask to guarantee you enter the door to paradise?

If eleven plus two equals one, what does nine plus five equal?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Rearrange the letters in "new door" to make one word.

Can you decipher the below rebus?

PBLUESAISNUERSES

How can you leave a room with two legs and return with six legs?

How can you take 2 from 5 and leave 4?

What is the end of everything?

A beggar on the street can make one cigarette out of every 6 cigarette butts he finds. After one whole day of searching and checking public ashtrays the beggar finds a total of 72 cigarette butts. How many cigarettes can he make and smoke from the butts he found?