Replace the question mark with the number below given a simple math problem.

When it's bad luck to meet a black cat?

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?

Replace the question mark with the correct number.

What has many teeth, but cannot bite?

Can you place six X (crosses) in below board without making three in a row in any way ?

How is the moon similar to a dollar?

I am first found in caves, now prolific online; I am a depiction, a drawing, a symbol, or sign. I will convey whichever mood you could wish; or for that matter, a fist, flask, or fish. What am I?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

Count the number of triangles in the below picture?