What country can make you shiver?

If we tell you that there is a relation between the numbers and letters in the given figure, can you analyze it and find the missing letter in the last box?

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

There are three boxes on a table. One of the box contains Gold and the other two are empty. A printed message contains in each box. One of the message is true and the other two are lies.

The first box says "The Gold is not here".

The Second box says "The Gold is not here".

The Third box says "The Gold is in the Second box".

Which box has the Gold?

Below toothpicks/matchsticks indicate the group of fishes moving from west to east direction. Can you make them move from east to west by just moving three toothpicks/matchsticks?

Which letter of the alphabet has the most water?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

How can a man go eight days without sleep?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?