Count the number of triangles in the below picture?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

If in a code language, DISTANCE is written as IDTUBECN and DOCUMENT is written as ODDVNTNE, the how will THURSDAY be coded as in the same language?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

In the picture, you can see a chess board. On the top left position, the K marks a knight. Now, can you move the knight in a manner that after 63 moves, the knight has been placed at all the squares exactly once excluding the starting square?

Can you complete the sequence?

192, 021, 222, 324, 252, 627, 2__, 9__?

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

What is the fastest way to double your money?

I am a type of word that is spelt incorrectly or used differently, on purpose for humour. What am I?
Hint 1: You can find me in a joke.
Hint 2: I am a play on words.