You were given nine same looking coins of which one is fake – weighs less. You can use even arm balance. How do you find out which coin is fake in two scalings?

Five pirates stole a treasure – exactly hundred gold coins.

Pirates have a special way of dividing their loot:

• The oldest one suggests how he would split up the loot.
• Everyone votes.
• If he gets more than half votes they split the loot according to his proposal.
• If he doesn’t the others kill him and the process starts all over again – without the dead pirate.

All pirates are very used to this way of dividing and they never break the rules. Everyone’s top priority is his life. Second is money. And if there is no money or life involved in his decision he likes to harm the others.

How will they split the loot?

As it often happens in life evil warlock imprisoned a wise man. Surprisingly he gave him a chance to save himself if he fulfils one task.

There is a round tray on the table which can be turned around freely. There are four coins on the tray placed as corners of a square.

Wiseman has his eyes covered so he doesn’t see anything. His task is to turn the coins so that they are all heads up.

He is not in easy situation. He may turn some coins and than the warlock will turn the tray around. He turns some coins again warlock turns the tray again. It goes on until all coins are turned correctly. At that moment evil warlock ends the game.

Wiseman can’t recognize one side from the other by touching it. He has to leave the coins where they were in the corners of a square. And mainly – because of the evil magic – he has the worst luck so if he relies just on chance he will never fulfill the task.

Imagine you want to send a valuable item to your friend. You have big enough box on which you can place several padlocks. You both have enough padlocks but the problem is that you don’t have keys to padlocks of the other one.

How do you send the valuable item so that it doesn’t go unlocked? Sending just a key doesn’t help because someone could replicate it.

Group of friends is trapped in a burning house. The house is going to collapse in 12 minutes so they desperately want to get out. They have to run through a hallway which is in flames. If someone wants to pass through he has to have a fire extinguisher to hold the flames back at least a little. Problem is that the friends have only one.

Only two people can go at once. Than somebody has to return with the extinguisher and other two can go.

There is one fireman among the friends who moves through flames with ease and he can ran through the hallway in one minute. His best friend who is in great shape can run through in 2 minutes. There is an older man who needs four minutes and a drunken guy who will need 5 minutes to pass through. If two people go together they move at speed of the slower one.

How will they do it so that they all get out before the house collapses?