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

How many times do a clock's hands overlap in a day ?

Name a key which is hardest to turn.

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

Which statement is true out of the following?
One statement here is false.
Two statements here are false.
Three statements here are false.

Jenifer and Jesica are having a conversation.

Jenifer: I am definitely not over 30.
Jesica: I am 28 and you are surely 5 years older to me at least.
Jenifer: No, you are at least 29.

You are told that both of them are lying throughout in the conversation. Can you find their respective ages?

You bought me for dinner but never eat me. What am I?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

In the given figure, you can see that four match sticks are used to form a square. Can you form five squares by using six matches?

There are two guys standing face to face in a room. On a wall, there is a clock. One of those is a prophet. He tells the other guy that he will be stabbed in the back in five minutes.

Shocked to hear that, the other guy stares at the clock. Just after the five minutes, he is stabbed on the back. Can you tell what happened?