Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

I am a number I am not an odd number I am higher than 90 I am not higher than 100 If you subtract me from 100, you get nothing. What number am I?

A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?

Count the number of triangles in the picture below:

John asked Jack, "The time right now is 7 pm. Can you tell me what will be the time 23, 999, 995 hours later ?"

While Bella does not know the answer, do you ?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

You are stuck on an island where you have nothing. You find four pieces of paper somewhere on the island. What will be your strategy to escape from the island safely?

PS: No other resource is available to you on the island, neither can you build anything.

Take one out and scratch my head, I am now black but once was red. What am I?