What is black when you buy it, red when you use it, and gray when you throw it away?

Can you calculate the probability of getting a sum of six when a dice is thrown twice?

How can you take 2 from 5 and leave 4?

John and Jill are madly in love with each other. To remind Jill of his pure love, John wants to send her a ring by post but in their country where burglary is quite prominent, any package that is not locked comes under the risk of being stolen for the contents.

John and Jill possess many padlocks but neither one of them has the other key.

Can you find a way John can send the ring to Jill safely?

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

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?

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

There are five vowels (a, e, i, o, u) in the English language.
Can you tell us a word that contains all these vowels?