Riddles, brain puzzles and mathematical problems

[BAndrew]

This thread was made for those who like using their wits to solve riddles and problems.

Here's how it's done:

A person posts a riddle/problem and the others are trying to figure out the solution. Whoever founds the solution posts a new riddle* and the same procedure is redone.

*NOTE: If the person can't or doesn't want to post/share a problem after he has solved one then (s)he should simply say so and another person will do this.

I guess I have to start. Here goes:

Riddle 1
Chess Horses
The picture shows 2 white and 2 black horses placed in one section of the board. How we can exchange the positions of the white with the black horses?

Clarifications:

1.) Horses are allowed to move only within the block illustrated in figure.
2.) The movement of each horse must be the same as it does in chess, ie shape "Γ"
3.) A horse can overleap (jump above) other horses, but can not go to a square occupied by another horse.
4.) Give your movements using the numbers shown in each square.

Figure:



Long update: Use spoilers in your answers.

Good luck!