If 21x = 79x, what is the value of x?

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.

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

Before the start of the car race, John and Jacob have the same amount of fuel in their car. With this fuel, John can drive for 4 hours while Jacob can drive five hours.
After a time they realize that the amount of fuel left in John's car is 1/4th of the fuel in Jacob's.

For how long they are racing?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

Can you count the number of triangles in the given picture?

Complete the table series riddle by finding the number that can replace "??".

What 5-letter word typed in all capital letters can be read the same upside down?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?